[url_launcher] Add url_launcher_platform_interface package (#2217)

* [url_launcher] Add overridable platform

* Fix analyzer lints

* Run dartfmt

* Add a url_launcher_platform_interface package

* Disable tests temporarily

* Add license header

* Fix typo in test

* Add LICENSE file

* Respond to review comments

* Respond to review comments

Author: Harry Terkelsen

packages/url_launcher/url_launcher_platform_interface/LICENSE

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+// Copyright 2017 The Chromium Authors. All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//    * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

packages/url_launcher/url_launcher_platform_interface/README.md

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+# url_launcher_platform_interface
+
+A common platform interface for the [`url_launcher`][1] plugin.
+
+This interface allows platform-specific implementations of the `url_launcher`
+plugin, as well as the plugin itself, to ensure they are supporting the
+same interface.
+
+# Usage
+
+To implement a new platform-specific implementation of `url_launcher`, extend
+[`UrlLauncherPlatform`][2] with an implementation that performs the
+platform-specific behavior, and when you register your plugin, set the default
+`UrlLauncherPlatform` by calling
+`UrlLauncherPlatform.instance = MyPlatformUrlLauncher()`.
+
+# Note on breaking changes
+
+Strongly prefer non-breaking changes (such as adding a method to the interface)
+over breaking changes for this package.
+
+See https://flutter.dev/go/platform-interface-breaking-changes for a discussion
+on why a less-clean interface is preferable to a breaking change.
+
+[1]: ../url_launcher
+[2]: lib/url_launcher_platform_interface.dart

packages/url_launcher/url_launcher_platform_interface/lib/method_channel_url_launcher.dart

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+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:flutter/services.dart';
+import 'package:meta/meta.dart' show required;
+
+import 'url_launcher_platform_interface.dart';
+
+const MethodChannel _channel = MethodChannel('plugins.flutter.io/url_launcher');
+
+/// An implementation of [UrlLauncherPlatform] that uses method channels.
+class MethodChannelUrlLauncher extends UrlLauncherPlatform {
+  @override
+  Future<bool> canLaunch(String url) {
+    return _channel.invokeMethod<bool>(
+      'canLaunch',
+      <String, Object>{'url': url},
+    );
+  }
+
+  @override
+  Future<void> closeWebView() {
+    return _channel.invokeMethod<void>('closeWebView');
+  }
+
+  @override
+  Future<bool> launch(
+    String url, {
+    @required bool useSafariVC,
+    @required bool useWebView,
+    @required bool enableJavaScript,
+    @required bool enableDomStorage,
+    @required bool universalLinksOnly,
+    @required Map<String, String> headers,
+  }) {
+    return _channel.invokeMethod<bool>(
+      'launch',
+      <String, Object>{
+        'url': url,
+        'useSafariVC': useSafariVC,
+        'useWebView': useWebView,
+        'enableJavaScript': enableJavaScript,
+        'enableDomStorage': enableDomStorage,
+        'universalLinksOnly': universalLinksOnly,
+        'headers': headers,
+      },
+    );
+  }
+}

packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart

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+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:meta/meta.dart' show required;
+
+import 'method_channel_url_launcher.dart';
+
+/// The interface that implementations of url_launcher must implement.
+///
+/// Platform implementations that live in a separate package should extend this
+/// class rather than implement it as `url_launcher` does not consider newly
+/// added methods to be breaking changes. Extending this class (using `extends`)
+/// ensures that the subclass will get the default implementation, while
+/// platform implementations that `implements` this interface will be broken by
+/// newly added [UrlLauncherPlatform] methods.
+abstract class UrlLauncherPlatform {
+  /// The default instance of [UrlLauncherPlatform] to use.
+  ///
+  /// Platform-specific plugins should override this with their own
+  /// platform-specific class that extends [UrlLauncherPlatform] when they
+  /// register themselves.
+  ///
+  /// Defaults to [MethodChannelUrlLauncher].
+  static UrlLauncherPlatform instance = MethodChannelUrlLauncher();
+
+  /// Returns `true` if this platform is able to launch [url].
+  Future<bool> canLaunch(String url) {
+    throw UnimplementedError('canLaunch() has not been implemented.');
+  }
+
+  /// Returns `true` if the given [url] was successfully launched.
+  ///
+  /// For documentation on the other arguments, see the `launch` documentation
+  /// in `package:url_launcher/url_launcher.dart`.
+  Future<bool> launch(
+    String url, {
+    @required bool useSafariVC,
+    @required bool useWebView,
+    @required bool enableJavaScript,
+    @required bool enableDomStorage,
+    @required bool universalLinksOnly,
+    @required Map<String, String> headers,
+  }) {
+    throw UnimplementedError('launch() has not been implemented.');
+  }
+
+  /// Closes the WebView, if one was opened earlier by [launch].
+  Future<void> closeWebView() {
+    throw UnimplementedError('closeWebView() has not been implemented.');
+  }
+}

packages/url_launcher/url_launcher_platform_interface/pubspec.yaml

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+name: url_launcher_platform_interface
+description: A common platform interface for the url_launcher plugin.
+author: Flutter Team <[email protected]>
+homepage: https://github.com/flutter/plugins/tree/master/packages/url_launcher/url_launcher_platform_interface
+# NOTE: We strongly prefer non-breaking changes, even at the expense of a
+# less-clean API. See https://flutter.dev/go/platform-interface-breaking-changes
+version: 1.0.0
+
+dependencies:
+  flutter:
+    sdk: flutter
+  meta: ^1.0.5
+
+dev_dependencies:
+  flutter_test:
+    sdk: flutter
+
+environment:
+  sdk: ">=2.0.0-dev.28.0 <3.0.0"
+  flutter: ">=1.9.1+hotfix.4 <2.0.0"