Make sure we refer to 'stable', and not 'release' branch. (#23745)

packages/flutter_tools/lib/src/version.dart

diff --git a/packages/flutter_tools/lib/src/version.dart b/packages/flutter_tools/lib/src/version.dart
index 1262c57..c8a39dc 100644
--- a/packages/flutter_tools/lib/src/version.dart
+++ b/packages/flutter_tools/lib/src/version.dart
@@ -47,7 +47,7 @@
     'master',
     'dev',
     'beta',
-    'release',
+    'stable',
   ]);
 
   /// This maps old branch names to the names of branches that replaced them.
@@ -63,7 +63,7 @@
 
   String _channel;
   /// The channel is the upstream branch.
-  /// `master`, `dev`, `beta`, `release`; or old ones, like `alpha`, `hackathon`, ...
+  /// `master`, `dev`, `beta`, `stable`; or old ones, like `alpha`, `hackathon`, ...
   String get channel => _channel;
 
   /// The name of the local branch.

packages/flutter_tools/test/channel_test.dart

diff --git a/packages/flutter_tools/test/channel_test.dart b/packages/flutter_tools/test/channel_test.dart
index 96c2e92..a7bdf64 100644
--- a/packages/flutter_tools/test/channel_test.dart
+++ b/packages/flutter_tools/test/channel_test.dart
@@ -56,8 +56,10 @@
       final Process process = createMockProcess(
           stdout: 'origin/dev\n'
                   'origin/beta\n'
+                  'origin/stable\n'
                   'upstream/dev\n'
-                  'upstream/beta\n');
+                  'upstream/beta\n'
+                  'upstream/stable\n');
       when(mockProcessManager.start(
         <String>['git', 'branch', '-r'],
         workingDirectory: anyNamed('workingDirectory'),
@@ -83,7 +85,7 @@
         .where((String line) => line?.isNotEmpty == true)
         .skip(1); // remove `Flutter channels:` line
 
-      expect(rows, <String>['dev', 'beta']);
+      expect(rows, <String>['dev', 'beta', 'stable']);
     }, overrides: <Type, Generator>{
       ProcessManager: () => mockProcessManager,
     });
@@ -127,6 +129,40 @@
 
       expect(testLogger.statusText, contains("Switching to flutter channel 'beta'..."));
       expect(testLogger.errorText, hasLength(0));
+
+      when(mockProcessManager.start(
+        <String>['git', 'fetch'],
+        workingDirectory: anyNamed('workingDirectory'),
+        environment: anyNamed('environment'),
+      )).thenAnswer((_) => Future<Process>.value(createMockProcess()));
+      when(mockProcessManager.start(
+        <String>['git', 'show-ref', '--verify', '--quiet', 'refs/heads/stable'],
+        workingDirectory: anyNamed('workingDirectory'),
+        environment: anyNamed('environment'),
+      )).thenAnswer((_) => Future<Process>.value(createMockProcess()));
+      when(mockProcessManager.start(
+        <String>['git', 'checkout', 'stable', '--'],
+        workingDirectory: anyNamed('workingDirectory'),
+        environment: anyNamed('environment'),
+      )).thenAnswer((_) => Future<Process>.value(createMockProcess()));
+
+      await runner.run(<String>['channel', 'stable']);
+
+      verify(mockProcessManager.start(
+        <String>['git', 'fetch'],
+        workingDirectory: anyNamed('workingDirectory'),
+        environment: anyNamed('environment'),
+      )).called(1);
+      verify(mockProcessManager.start(
+        <String>['git', 'show-ref', '--verify', '--quiet', 'refs/heads/stable'],
+        workingDirectory: anyNamed('workingDirectory'),
+        environment: anyNamed('environment'),
+      )).called(1);
+      verify(mockProcessManager.start(
+        <String>['git', 'checkout', 'stable', '--'],
+        workingDirectory: anyNamed('workingDirectory'),
+        environment: anyNamed('environment'),
+      )).called(1);
     }, overrides: <Type, Generator>{
       ProcessManager: () => mockProcessManager,
       FileSystem: () => MemoryFileSystem(),