Add admin enforcement to protected branches API. (google#610)

This change adds support for an addition to the Protected Branches API
preview, the ability to turn on and off admin settings in one place.

This is documented at https://developer.github.com/changes/2017-03-22-protected-branches-admin-improvements/.

The IncludeAdmins fields are deprecated, but they're still required to
be sent in the request for now. A future update to API preview will
remove the IncludeAdmins fields completely.

Helps google#606.

Author: amirilovic

github/github-accessors.go

@@ -511,19 +511,22 @@ type Branch struct {
 type Protection struct {
 	RequiredStatusChecks       *RequiredStatusChecks       `json:"required_status_checks"`
 	RequiredPullRequestReviews *RequiredPullRequestReviews `json:"required_pull_request_reviews"`
+	EnforceAdmins              *AdminEnforcement           `json:"enforce_admins"`
 	Restrictions               *BranchRestrictions         `json:"restrictions"`
 }
 
 // ProtectionRequest represents a request to create/edit a branch's protection.
 type ProtectionRequest struct {
 	RequiredStatusChecks       *RequiredStatusChecks       `json:"required_status_checks"`
 	RequiredPullRequestReviews *RequiredPullRequestReviews `json:"required_pull_request_reviews"`
+	EnforceAdmins              bool                        `json:"enforce_admins"`
 	Restrictions               *BranchRestrictionsRequest  `json:"restrictions"`
 }
 
 // RequiredStatusChecks represents the protection status of a individual branch.
 type RequiredStatusChecks struct {
 	// Enforce required status checks for repository administrators. (Required.)
+	// Deprecated: Use EnforceAdmins instead.
 	IncludeAdmins bool `json:"include_admins"`
 	// Require branches to be up to date before merging. (Required.)
 	Strict bool `json:"strict"`
@@ -535,9 +538,16 @@ type RequiredStatusChecks struct {
 // RequiredPullRequestReviews represents the protection configuration for pull requests.
 type RequiredPullRequestReviews struct {
 	// Enforce pull request reviews for repository administrators. (Required.)
+	// Deprecated: Use EnforceAdmins instead.
 	IncludeAdmins bool `json:"include_admins"`
 }
 
+// AdminEnforcement represents the configuration to enforce required status checks for repository administrators.
+type AdminEnforcement struct {
+	URL     *string `json:"url,omitempty"`
+	Enabled bool    `json:"enabled"`
+}
+
 // BranchRestrictions represents the restriction that only certain users or
 // teams may push to a branch.
 type BranchRestrictions struct {

github/repos.go

@@ -482,7 +482,7 @@ func TestRepositoriesService_GetBranchProtection(t *testing.T) {
 
 		testMethod(t, r, "GET")
 		testHeader(t, r, "Accept", mediaTypeProtectedBranchesPreview)
-		fmt.Fprintf(w, `{"required_status_checks":{"include_admins":true,"strict":true,"contexts":["continuous-integration"]},"required_pull_request_reviews":{"include_admins":true},"restrictions":{"users":[{"id":1,"login":"u"}],"teams":[{"id":2,"slug":"t"}]}}`)
+		fmt.Fprintf(w, `{"required_status_checks":{"include_admins":true,"strict":true,"contexts":["continuous-integration"]},"required_pull_request_reviews":{"include_admins":true},"enforce_admins":{"url":"/repos/o/r/branches/b/protection/enforce_admins","enabled":true},"restrictions":{"users":[{"id":1,"login":"u"}],"teams":[{"id":2,"slug":"t"}]}}`)
 	})
 
 	protection, _, err := client.Repositories.GetBranchProtection(context.Background(), "o", "r", "b")
@@ -499,6 +499,10 @@ func TestRepositoriesService_GetBranchProtection(t *testing.T) {
 		RequiredPullRequestReviews: &RequiredPullRequestReviews{
 			IncludeAdmins: true,
 		},
+		EnforceAdmins: &AdminEnforcement{
+			URL:     String("/repos/o/r/branches/b/protection/enforce_admins"),
+			Enabled: true,
+		},
 		Restrictions: &BranchRestrictions{
 			Users: []*User{
 				{Login: String("u"), ID: Int(1)},