Add a flag to enable tracing to systrace. (#27208)

packages/flutter_tools/lib/src/android/android_device.dart

@@ -428,6 +428,8 @@ class AndroidDevice extends Device {
       cmd.addAll(<String>['--ez', 'skia-deterministic-rendering', 'true']);
     if (debuggingOptions.traceSkia)
       cmd.addAll(<String>['--ez', 'trace-skia', 'true']);
+    if (debuggingOptions.traceSystrace)
+      cmd.addAll(<String>['--ez', 'trace-systrace', 'true']);
     if (debuggingOptions.debuggingEnabled) {
       if (debuggingOptions.buildInfo.isDebug)
         cmd.addAll(<String>['--ez', 'enable-checked-mode', 'true']);

packages/flutter_tools/lib/src/commands/run.dart

@@ -90,6 +90,11 @@ class RunCommand extends RunCommandBase {
         help: 'Enable tracing of Skia code. This is useful when debugging '
               'the GPU thread. By default, Flutter will not log skia code.',
       )
+      ..addFlag('trace-systrace',
+        negatable: false,
+        help: 'Enable tracing to the system tracer. This is only useful on '
+              'platforms where such a tracer is available (Android and Fuchsia).',
+      )
       ..addFlag('await-first-frame-when-tracing',
         defaultsTo: true,
         help: 'Whether to wait for the first frame when tracing startup ("--trace-startup"), '
@@ -249,6 +254,7 @@ class RunCommand extends RunCommandBase {
         enableSoftwareRendering: argResults['enable-software-rendering'],
         skiaDeterministicRendering: argResults['skia-deterministic-rendering'],
         traceSkia: argResults['trace-skia'],
+        traceSystrace: argResults['trace-systrace'],
         observatoryPort: observatoryPort,
       );
     }

packages/flutter_tools/lib/src/device.dart

@@ -356,6 +356,7 @@ class DebuggingOptions {
     this.enableSoftwareRendering = false,
     this.skiaDeterministicRendering = false,
     this.traceSkia = false,
+    this.traceSystrace = false,
     this.useTestFonts = false,
     this.observatoryPort,
    }) : debuggingEnabled = true;
@@ -367,6 +368,7 @@ class DebuggingOptions {
     enableSoftwareRendering = false,
     skiaDeterministicRendering = false,
     traceSkia = false,
+    traceSystrace = false,
     observatoryPort = null;
 
   final bool debuggingEnabled;
@@ -376,6 +378,7 @@ class DebuggingOptions {
   final bool enableSoftwareRendering;
   final bool skiaDeterministicRendering;
   final bool traceSkia;
+  final bool traceSystrace;
   final bool useTestFonts;
   final int observatoryPort;