Android: Browser-side scheduling latency tweaks

content/browser/renderer_host/compositor_impl_android.cc

Index: content/browser/renderer_host/compositor_impl_android.cc
diff --git a/content/browser/renderer_host/compositor_impl_android.cc b/content/browser/renderer_host/compositor_impl_android.cc
index 56b9201dcc5b70abac801a1e398ffac1b25a33d9..a34da7218e20ff43f780cd52c437e41db3f9a8c4 100644
--- a/content/browser/renderer_host/compositor_impl_android.cc
+++ b/content/browser/renderer_host/compositor_impl_android.cc
@@ -160,7 +160,7 @@ class ExternalBeginFrameSource : public cc::BeginFrameSourceBase,
                                  public CompositorImpl::VSyncObserver {
  public:
   ExternalBeginFrameSource(CompositorImpl* compositor)
-      : compositor_(compositor) {
+      : compositor_(compositor), needs_begin_frames_(false) {
     compositor_->AddObserver(this);
   }
 
@@ -170,19 +170,41 @@ class ExternalBeginFrameSource : public cc::BeginFrameSourceBase,
 
   // cc::BeginFrameSourceBase implementation:
   void OnNeedsBeginFramesChanged(bool needs_begin_frames) override {
+    TRACE_EVENT1("compositor", "OnNeedsBeginFramesChanged",
+                 "needs_begin_frames", needs_begin_frames);
     compositor_->OnNeedsBeginFramesChange(needs_begin_frames);
+    needs_begin_frames_ = needs_begin_frames;
+    if (needs_begin_frames) {

[no sievers, 2016/04/11 23:10:10]

Oh I was going to ask:

Should I also remember the last vsync to make sure that we didn't already send a
BeginFrame() this interval, or can this not happen (or rather does not matter)
because the scheduler would have not drawn for a frame if it previously turned
off BeginFrames?

+      base::TimeTicks now = base::TimeTicks::Now();
+      // Since |needs_begin_frames_| turned on, the scheduler wants to draw,
+      // so the dealine doesn't matter much. But pass something large enough
+      // to make sure we don't get discarded in BeginRetroFrame(), see
+      // crbug.com/602485.
+      base::TimeTicks deadline = now + base::TimeDelta::FromMilliseconds(16);
+      cc::BeginFrameArgs args(cc::BeginFrameArgs::Create(
+          BEGINFRAME_FROM_HERE, now, deadline,
+          base::TimeDelta::FromMilliseconds(16), cc::BeginFrameArgs::NORMAL));
+      base::Closure tick =
+          base::Bind(&ExternalBeginFrameSource::CallOnBeginFrame,
+                     base::Unretained(this), args);
+      base::ThreadTaskRunnerHandle::Get()->PostTask(FROM_HERE, tick);
+    }
   }
 
   // CompositorImpl::VSyncObserver implementation:
   void OnVSync(base::TimeTicks frame_time,
                base::TimeDelta vsync_period) override {
-    CallOnBeginFrame(cc::BeginFrameArgs::Create(
-        BEGINFRAME_FROM_HERE, frame_time, base::TimeTicks::Now(), vsync_period,
-        cc::BeginFrameArgs::NORMAL));
+    base::TimeTicks deadline = frame_time + 2 * vsync_period / 3;
+    if (needs_begin_frames_) {
+      CallOnBeginFrame(
+          cc::BeginFrameArgs::Create(BEGINFRAME_FROM_HERE, frame_time, deadline,
+                                     vsync_period, cc::BeginFrameArgs::NORMAL));
+    }
   }
 
  private:
   CompositorImpl* compositor_;
+  bool needs_begin_frames_;
 };
 
 static bool g_initialized = false;
@@ -406,6 +428,7 @@ void CompositorImpl::SetHasTransparentBackground(bool flag) {
 void CompositorImpl::SetNeedsComposite() {
   if (!host_->visible())
     return;
+  TRACE_EVENT0("compositor", "Compositor::SetNeedsComposite");
   host_->SetNeedsAnimate();
 }
 
@@ -585,10 +608,12 @@ void CompositorImpl::RemoveObserver(VSyncObserver* observer) {
 
 cc::UIResourceId CompositorImpl::CreateUIResource(
     cc::UIResourceClient* client) {
+  TRACE_EVENT0("compositor", "CompositorImpl::CreateUIResource");
   return host_->CreateUIResource(client);
 }
 
 void CompositorImpl::DeleteUIResource(cc::UIResourceId resource_id) {
+  TRACE_EVENT0("compositor", "CompositorImpl::DeleteUIResource");
   host_->DeleteUIResource(resource_id);
 }
 
@@ -649,6 +674,7 @@ void CompositorImpl::SetNeedsAnimate() {
   if (!host_->visible())
     return;
 
+  TRACE_EVENT0("compositor", "Compositor::SetNeedsAnimate");
   host_->SetNeedsAnimate();
 }