Add scope handling methods to google_sign_in_web.

packages/google_sign_in/google_sign_in_web/lib/google_sign_in_web.dart

@@ -176,4 +176,29 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
 
     return auth2.getAuthInstance().disconnect();
   }
+
+  @override
+  Future<bool> hasGrantedScope(String scope) async {
+    await initialized;
+
+    return auth2
+            .getAuthInstance()
+            ?.currentUser
+            ?.get()
+            ?.getGrantedScopes()
+            ?.contains(scope) ??
+        false;
+  }
+
+  @override
+  Future<bool> requestScope(String scope) async {
+    await initialized;
+
+    return auth2
+            .getAuthInstance()
+            ?.currentUser
+            ?.get()
+            ?.grant(auth2.SigninOptions(scope: scope)) ??
+        false;
+  }
 }

packages/google_sign_in/google_sign_in_web/test/auth2_test.dart

@@ -73,5 +73,17 @@ void main() {
 
       expect(actualToken, expectedTokenData);
     });
+
+    test('hasGrantedScope', () async {
+      bool hasScope = await plugin.hasGrantedScope('scope');
+
+      expect(hasScope, isTrue);
+    });
+
+    test('requestScope', () async {
+      bool scopeGranted = await plugin.requestScope('newScope');
+
+      expect(scopeGranted, isTrue);
+    });
   });
 }

packages/google_sign_in/google_sign_in_web/test/gapi_mocks/src/google_user.dart

@@ -21,5 +21,7 @@ String googleUser(GoogleSignInUserData data) => '''
       access_token: 'access_${data.idToken}',
     }
   },
+  getGrantedScopes: () => 'some scope',
+  grant: () => true,
 }
 ''';