compositor worker: Use a WebThread for the compositor thread.

content/child/blink_platform_impl.cc

Index: content/child/blink_platform_impl.cc
diff --git a/content/child/blink_platform_impl.cc b/content/child/blink_platform_impl.cc
index 75ac1489d92152578b6eb70a33921fcf3ad52010..68c748fcbc6e67e9c049d90edf06c632c0eb0e33 100644
--- a/content/child/blink_platform_impl.cc
+++ b/content/child/blink_platform_impl.cc
@@ -37,6 +37,7 @@
 #include "components/mime_util/mime_util.h"
 #include "components/scheduler/child/web_task_runner_impl.h"
 #include "components/scheduler/child/webthread_impl_for_worker_scheduler.h"
+#include "components/scheduler/child/worker_scheduler.h"
 #include "content/app/resources/grit/content_resources.h"
 #include "content/app/strings/grit/content_strings.h"
 #include "content/child/background_sync/background_sync_provider.h"
@@ -89,6 +90,43 @@ namespace content {
 
 namespace {
 
+class CompositorWorkerScheduler : public scheduler::WorkerScheduler {

[Sami, 2016/01/14 13:55:05]

Would you mind putting this to
components/scheduler/renderer/compositor_worker_scheduler.{cc,h} instead? Right
now there's not much here but I think we might want to integrate this more
closely with the other scheduling machinery in the future.

[sadrul, 2016/01/14 15:20:40]

Done (moved to */child/* instead of in */renderer/* since this is going to be
used from here in content/child/).

+ public:
+  explicit CompositorWorkerScheduler(base::Thread* thread) : thread_(thread) {}
+  ~CompositorWorkerScheduler() override {}
+
+  // WorkerScheduler:
+  scoped_refptr<base::SingleThreadTaskRunner> DefaultTaskRunner() override {
+    return thread_->task_runner();

[Sami, 2016/01/14 13:55:05]

If we do decide to land this pass through scheduler as a first step, could you
add a TODO here for adding an actual scheduler here and making sure performance
does not regress?

[sadrul, 2016/01/14 15:20:40]

Done.

+  }
+
+  scoped_refptr<scheduler::SingleThreadIdleTaskRunner> IdleTaskRunner()
+      override {
+    return nullptr;

[Sami, 2016/01/14 13:55:05]

Presumably the compositor worker will need to do some garbage collection at some
point? This is normally done using idle tasks, but if we don't support them v8
falls back to inline GC, which might cause janks. That might be fine for now,
but let's at least have a TODO here mentioning this.

[sadrul, 2016/01/14 15:20:40]

Done.

+  }
+
+  bool CanExceedIdleDeadlineIfRequired() const override { return false; }
+
+  bool ShouldYieldForHighPriorityWork() override { return false; }
+
+  void AddTaskObserver(
+      base::MessageLoop::TaskObserver* task_observer) override {
+    thread_->message_loop()->AddTaskObserver(task_observer);
+  }
+
+  void RemoveTaskObserver(
+      base::MessageLoop::TaskObserver* task_observer) override {
+    thread_->message_loop()->RemoveTaskObserver(task_observer);
+  }
+
+  void Init() override {}
+  void Shutdown() override {}
+
+ private:
+  base::Thread* thread_;
+  DISALLOW_COPY_AND_ASSIGN(CompositorWorkerScheduler);
+};
+
 class WebThreadForCompositor : public WebThreadImplForWorkerScheduler {
  public:
   explicit WebThreadForCompositor(base::Thread::Options options)
@@ -99,7 +137,9 @@ class WebThreadForCompositor : public WebThreadImplForWorkerScheduler {
 
  private:
   // WebThreadImplForWorkerScheduler:
-  bool UseThreadTaskRunnerAsDefault() const override { return true; }
+  scoped_ptr<scheduler::WorkerScheduler> CreateWorkerScheduler() override {
+    return make_scoped_ptr(new CompositorWorkerScheduler(thread()));
+  }
 
   DISALLOW_COPY_AND_ASSIGN(WebThreadForCompositor);
 };