[flutter_tools] fix screenshot command in release mode and help documentation (#65114)

Currently taking a screenshot in release mode crashes and is also not documented as a supported command. Fix both of these and add test cases.

packages/flutter_tools/lib/src/resident_runner.dart

@@ -1102,20 +1102,29 @@ abstract class ResidentRunner {
       'flutter',
       'png',
     );
-    final List<FlutterView> views = await device
-      .vmService.getFlutterViews();
-    try {
-      if (supportsServiceProtocol && isRunningDebug) {
+    List<FlutterView> views = <FlutterView>[];
+    Future<bool> setDebugBanner(bool value) async {
       try {
         for (final FlutterView view in views) {
           await device.vmService.flutterDebugAllowBanner(
-              false,
+            value,
             isolateId: view.uiIsolate.id,
           );
         }
+        return true;
       } on Exception catch (error) {
         status.cancel();
         globals.printError('Error communicating with Flutter on the device: $error');
+        return false;
+      }
+    }
+
+    try {
+      if (supportsServiceProtocol && isRunningDebug) {
+        // Ensure that the vmService access is guarded by supportsServiceProtocol, it
+        // will be null in release mode.
+        views = await device.vmService.getFlutterViews();
+        if (!await setDebugBanner(false)) {
           return;
         }
       }
@@ -1123,18 +1132,7 @@ abstract class ResidentRunner {
         await device.device.takeScreenshot(outputFile);
       } finally {
         if (supportsServiceProtocol && isRunningDebug) {
-          try {
-            for (final FlutterView view in views) {
-              await device.vmService.flutterDebugAllowBanner(
-                true,
-                isolateId: view.uiIsolate.id,
-              );
-            }
-          } on Exception catch (error) {
-            status.cancel();
-            globals.printError('Error communicating with Flutter on the device: $error');
-            return;
-          }
+          await setDebugBanner(true);
         }
       }
       final int sizeKB = outputFile.lengthSync() ~/ 1024;

packages/flutter_tools/lib/src/run_cold.dart

@@ -185,11 +185,9 @@ class ColdRunner extends ResidentRunner {
   @override
   void printHelp({ @required bool details }) {
     globals.printStatus('Flutter run key commands.');
-    if (supportsServiceProtocol) {
     if (details) {
       printHelpDetails();
     }
-    }
     commandHelp.h.print();
     if (_didAttach) {
       commandHelp.d.print();

packages/flutter_tools/test/general.shard/resident_runner_test.dart

@@ -188,7 +188,7 @@ void main() {
         return testUri;
       });
     when(mockFlutterDevice.vmService).thenAnswer((Invocation invocation) {
-      return fakeVmServiceHost.vmService;
+      return fakeVmServiceHost?.vmService;
     });
     when(mockFlutterDevice.reloadSources(any, pause: anyNamed('pause'))).thenAnswer((Invocation invocation) async {
       return <Future<vm_service.ReloadReport>>[
@@ -1289,6 +1289,42 @@ void main() {
     ));
   }));
 
+  testUsingContext('ResidentRunner printHelpDetails cold runner', () => testbed.run(() {
+    when(mockDevice.supportsHotRestart).thenReturn(true);
+    when(mockDevice.supportsScreenshot).thenReturn(true);
+    fakeVmServiceHost = null;
+    residentRunner = ColdRunner(
+      <FlutterDevice>[
+        mockFlutterDevice,
+      ],
+      stayResident: false,
+      debuggingOptions: DebuggingOptions.disabled(BuildInfo.release),
+    );
+    residentRunner.printHelp(details: true);
+
+    final CommandHelp commandHelp = residentRunner.commandHelp;
+
+    // does not supports service protocol
+    expect(residentRunner.supportsServiceProtocol, false);
+    // isRunningDebug
+    expect(residentRunner.isRunningDebug, false);
+    // does not support CanvasKit
+    expect(residentRunner.supportsCanvasKit, false);
+    // does support SkSL
+    expect(residentRunner.supportsWriteSkSL, false);
+    // commands
+    expect(testLogger.statusText, equals(
+        <dynamic>[
+          'Flutter run key commands.',
+          commandHelp.s,
+          commandHelp.h,
+          commandHelp.c,
+          commandHelp.q,
+          ''
+        ].join('\n')
+    ));
+  }));
+
   testUsingContext('ResidentRunner does support CanvasKit', () => testbed.run(() async {
     fakeVmServiceHost = FakeVmServiceHost(requests: <VmServiceExpectation>[]);
 
@@ -1395,6 +1431,26 @@ void main() {
     expect(fakeVmServiceHost.hasRemainingExpectations, false);
   }));
 
+  testUsingContext('ResidentRunner can take screenshot on release device', () => testbed.run(() async {
+    when(mockDevice.supportsScreenshot).thenReturn(true);
+    when(mockDevice.takeScreenshot(any))
+      .thenAnswer((Invocation invocation) async {
+        final File file = invocation.positionalArguments.first as File;
+        file.writeAsBytesSync(List<int>.generate(1024, (int i) => i));
+      });
+
+    residentRunner = ColdRunner(
+      <FlutterDevice>[
+        mockFlutterDevice,
+      ],
+      stayResident: false,
+      debuggingOptions: DebuggingOptions.disabled(BuildInfo.release),
+    );
+    await residentRunner.screenshot(mockFlutterDevice);
+
+    expect(testLogger.statusText, contains('1kB'));
+  }));
+
   testUsingContext('ResidentRunner clears the screen when it should', () => testbed.run(() async {
     fakeVmServiceHost = FakeVmServiceHost(requests: <VmServiceExpectation>[]);
     const String message = 'This should be cleared';
@@ -1488,9 +1544,7 @@ void main() {
   }));
 
   testUsingContext('ResidentRunner does not toggle banner in non-debug mode', () => testbed.run(() async {
-    fakeVmServiceHost = FakeVmServiceHost(requests: <VmServiceExpectation>[
-      listViews,
-    ]);
+    fakeVmServiceHost = FakeVmServiceHost(requests: <VmServiceExpectation>[]);
     residentRunner = HotRunner(
       <FlutterDevice>[
         mockFlutterDevice,