services/ui: Detect when a video is playing

services/ui/ws/frame_generator.cc

Index: services/ui/ws/frame_generator.cc
diff --git a/services/ui/ws/frame_generator.cc b/services/ui/ws/frame_generator.cc
index 81a29c86ed22f6edaa367f59bbc197b52f26304d..0aa3f8c1c2f4a104b9f6cf28c2c11a3badb09544 100644
--- a/services/ui/ws/frame_generator.cc
+++ b/services/ui/ws/frame_generator.cc
@@ -73,7 +73,15 @@ void FrameGenerator::Draw() {
     return;
 
   // TODO(fsamuel): We should add a trace for generating a top level frame.
+  bool old_contains_video = may_contain_video_;
   cc::CompositorFrame frame(GenerateCompositorFrame());

[sky, 2016/07/27 21:19:34]

It's mildly confusing that GenerateCompositorFrame and DrawWindowTree update
may_contain_video_. Can DrawWindowTree() take a boolean* that is set if there
may be video and this checks frame.meta.data.may_contain_video?

[sadrul, 2016/07/28 00:48:05]

Done (also made GenerateCompositorFrame() and DrawWindowTree() const methods)

+  if (old_contains_video != may_contain_video_) {
+    // TODO(sad): Schedule notifying observers.
+    if (may_contain_video_) {
+      // TODO(sad): Start a timer to reset the bit if no new frame with video
+      // is submitted 'soon'.
+    }
+  }
   frame_pending_ = true;
   if (display_compositor_) {
     display_compositor_->SubmitCompositorFrame(
@@ -99,6 +107,7 @@ cc::CompositorFrame FrameGenerator::GenerateCompositorFrame() {
   render_pass->SetNew(render_pass_id, output_rect, dirty_rect_,
                       gfx::Transform());
 
+  may_contain_video_ = false;
   DrawWindowTree(render_pass.get(), delegate_->GetRootWindow(), gfx::Vector2d(),
                  1.0f);
 
@@ -126,6 +135,7 @@ cc::CompositorFrame FrameGenerator::GenerateCompositorFrame() {
 
   cc::CompositorFrame frame;
   frame.delegated_frame_data = std::move(frame_data);
+  frame.metadata.may_contain_video = may_contain_video_;
   return frame;
 }
 
@@ -179,6 +189,8 @@ void FrameGenerator::DrawWindowTree(
                  gfx::Rect() /* opaque_rect */,
                  bounds_at_origin /* visible_rect */, true /* needs_blending*/,
                  default_surface->id());
+    if (default_surface->may_contain_video())
+      may_contain_video_ = true;
   }
   if (underlay_surface) {
     const gfx::Rect underlay_absolute_bounds =
@@ -201,6 +213,7 @@ void FrameGenerator::DrawWindowTree(
                  gfx::Rect() /* opaque_rect */,
                  bounds_at_origin /* visible_rect */, true /* needs_blending*/,
                  underlay_surface->id());
+    DCHECK(!underlay_surface->may_contain_video());
   }
 }