fix($location): support alternative means of setting application base path

In HTML, the <base> tag is used to configure how relative hyperlinks are resolved. In Angular, it
has another use, configuring how URLs are rewritten. Because of this, setting the base URL to some
external path outside of the application would cause $location.$$parse() to throw (which is the
desired behaviour).

This change enables developers to imperatively configure the application basePath, taking advantage
of the natural HTML use of the <base> tag without breaking Angular applications.

Example:

```
angular.module("test", [])
  .config(function($locationProvider) {
    $locationProvider.baseHref("http://foo.com/the/base/application/path/");
  });
```

Closes angular#4442

Author: caitp

src/ng/browser.js

@@ -1,4 +1,5 @@
 'use strict';
+var BASE_HREF_REGEXP = /^(https?\:)?\/\/[^\/]*/;
 
 /**
  * ! This is a private undocumented service !
@@ -253,7 +254,7 @@ function Browser(window, document, $log, $sniffer) {
    */
   self.baseHref = function() {
     var href = baseElement.attr('href');
-    return href ? href.replace(/^(https?\:)?\/\/[^\/]*/, '') : '';
+    return href ? href.replace(BASE_HREF_REGEXP, '') : '';
   };
 
   //////////////////////////////////////////////////////////////

src/ng/location.js

@@ -531,7 +531,8 @@ function locationGetterSetter(property, preprocess) {
  */
 function $LocationProvider(){
   var hashPrefix = '',
-      html5Mode = false;
+      html5Mode = false,
+      _baseHref;
 
   /**
    * @ngdoc property
@@ -567,6 +568,22 @@ function $LocationProvider(){
     }
   };
 
+  /**
+   * @ngdoc property
+   * @name ng.$locationProvider#baseHref
+   * @methodOf ng.$locationProvider
+   * @description
+   * In situations where it is desireable to specify an external URL within the `<base>` tag, for
+   * simplifying access to external resources, this configuration method will override the <base>
+   * tag and enable location rewrites to work as expected;
+   * 
+   * @param {string} href Base application url
+   */
+  this.baseHref = function(href) {
+    /* global BASE_HREF_REGEXP */
+    _baseHref = href && href.replace(BASE_HREF_REGEXP, '');
+  };
+
   /**
    * @ngdoc event
    * @name ng.$location#$locationChangeStart
@@ -600,7 +617,8 @@ function $LocationProvider(){
       function( $rootScope,   $browser,   $sniffer,   $rootElement) {
     var $location,
         LocationMode,
-        baseHref = $browser.baseHref(), // if base[href] is undefined, it defaults to ''
+        // if base[href] is undefined, it defaults to ''
+        baseHref = isString(_baseHref) ? _baseHref : $browser.baseHref(),
         initialUrl = $browser.url(),
         appBase;
 

test/ng/locationSpec.js

@@ -1256,6 +1256,23 @@ describe('$location', function() {
         }).not.toThrow();
       });
     });
+
+
+    it('should use $locationProvider.baseHref() as base url if available', function() {
+      module(function($locationProvider) {
+        $locationProvider.baseHref("http://host.com/ngApp/");
+        $locationProvider.html5Mode(true);
+        return function($browser, $rootElement, $document){
+          $browser.url("http://host.com/ngApp/");
+          $browser.$$baseHref = "http://server/assets";
+        };
+      });
+
+      inject(function($rootScope, $location, $browser) {
+        expect(function() { $location.$$parse($location.$$rewrite("http://host.com/ngApp/routeA")); }).not.toThrow();
+        expect($location.path()).toBe('/routeA');       
+      });
+    });
   });