services/ui: Detect when a video is playing

cc/surfaces/surface_aggregator.cc

Index: cc/surfaces/surface_aggregator.cc
diff --git a/cc/surfaces/surface_aggregator.cc b/cc/surfaces/surface_aggregator.cc
index f4681466f26aecd04c396595e05641969b20d671..b6b9fa668fcc9fac0b151d497e74dac47d16b96c 100644
--- a/cc/surfaces/surface_aggregator.cc
+++ b/cc/surfaces/surface_aggregator.cc
@@ -702,6 +702,8 @@ gfx::Rect SurfaceAggregator::PrewalkTree(const SurfaceId& surface_id,
   }
 
   referenced_surfaces_.erase(it);
+  if (!damage_rect.IsEmpty() && surface_frame.metadata.may_contain_video)

[enne (OOO), 2016/07/25 19:17:35]

Why does the damage rect come into play here? If you had a 30 fps video but the
browser compositor had a tab spinner animation at 60fps, would you want the may
contain video to alternate true/false every other frame?

[sadrul, 2016/07/26 04:39:20]

Yes. The window server will need to notify observers of inactivity based on a
timeout anyway (e.g. if a video is paused, and no new frame is submitted, we
need to notify that video has stopped playing). So if the flag is toggled every
frame, that wouldn't be problematic here.

[enne (OOO), 2016/07/26 21:43:54]

Hmm, makes sense for paused videos, thanks for the explanation.

+    result->may_contain_video = true;
   return damage_rect;
 }
 
@@ -786,6 +788,7 @@ CompositorFrame SurfaceAggregator::Aggregate(const SurfaceId& surface_id) {
       PrewalkTree(surface_id, false, RenderPassId(), &prewalk_result);
   PropagateCopyRequestPasses();
   has_copy_requests_ = !copy_request_passes_.empty();
+  frame.metadata.may_contain_video = prewalk_result.may_contain_video;
 
   CopyUndrawnSurfaces(&prewalk_result);
   SurfaceSet::iterator it = referenced_surfaces_.insert(surface_id).first;