services/ui: Detect when a video is playing

cc/proto/layer.proto

Index: cc/proto/layer.proto
diff --git a/cc/proto/layer.proto b/cc/proto/layer.proto
index c8ae18b85d081cacd125b25de0799e12cfde2fd9..9a0ce5d80146d22becc47abb5d7e0aa139afd087 100644
--- a/cc/proto/layer.proto
+++ b/cc/proto/layer.proto
@@ -67,7 +67,7 @@ message LayerProperties {
   optional SolidColorScrollbarLayerProperties solid_scrollbar = 7;
 }
 
-// NEXT ID: 55
+// NEXT ID: 56
 message BaseLayerProperties {
   optional Point3F transform_origin = 1;
   optional uint32 background_color = 2;
@@ -80,6 +80,7 @@ message BaseLayerProperties {
   optional Vector2dF offset_to_transform_parent = 7;
   optional bool double_sided = 8;
   optional bool draws_content = 9;
+  optional bool may_contain_video = 55;
   optional bool hide_layer_and_subtree = 10;
   optional bool subtree_property_changed = 47;
   optional bool layer_property_changed = 54;