cc: Introduce BeginFrame sequence numbers and acknowledgements.

content/browser/renderer_host/render_widget_host_view_aura.cc

Index: content/browser/renderer_host/render_widget_host_view_aura.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_aura.cc b/content/browser/renderer_host/render_widget_host_view_aura.cc
index a762af3d07b90ffde7aa976afbd69d9776720f49..d7fa1b27d3347d168779963b7d5baf26f91c6c6d 100644
--- a/content/browser/renderer_host/render_widget_host_view_aura.cc
+++ b/content/browser/renderer_host/render_widget_host_view_aura.cc
@@ -370,6 +370,7 @@ RenderWidgetHostViewAura::RenderWidgetHostViewAura(RenderWidgetHost* host,
       is_loading_(false),
       has_composition_text_(false),
       begin_frame_source_(nullptr),
+      oldest_incorporated_frame_(0),
       needs_begin_frames_(false),
       needs_flush_input_(false),
       added_frame_observer_(false),
@@ -676,8 +677,13 @@ void RenderWidgetHostViewAura::UpdateNeedsBeginFramesInternal() {
     begin_frame_source_->RemoveObserver(this);
 }
 
-void RenderWidgetHostViewAura::OnBeginFrame(
-    const cc::BeginFrameArgs& args) {
+void RenderWidgetHostViewAura::OnBeginFrame(const cc::BeginFrameArgs& args) {
+  if (args.source_id != last_begin_frame_args_.source_id) {
+    // Consider us up to date up to the previous BeginFrame.
+    oldest_incorporated_frame_ =
+        args.sequence_number > 0 ? args.sequence_number - 1 : 0;
+  }
+
   needs_flush_input_ = false;
   host_->FlushInput();
   UpdateNeedsBeginFramesInternal();
@@ -935,10 +941,33 @@ void RenderWidgetHostViewAura::OnSwapCompositorFrame(
     selection.end.SetEdge(end_edge_top, end_edge_bottom);
   }
 
+  uint64_t begin_frame_source_id = frame.metadata.begin_frame_source_id;
+  uint64_t begin_frame_number = frame.metadata.begin_frame_number;
+  uint64_t oldest_incorporated_frame = frame.metadata.oldest_incorporated_frame;
+
   delegated_frame_host_->SwapDelegatedFrame(compositor_frame_sink_id,
                                             std::move(frame));
   SelectionUpdated(selection.is_editable, selection.is_empty_text_form_control,
                    selection.start, selection.end);
+
+  // The CompositorFrame's updates were only incorporated if it wasn't skipped.
+  bool has_updates = false;
+  if (!delegated_frame_host_->skipped_frames()) {
+    oldest_incorporated_frame_ = oldest_incorporated_frame;
+    has_updates = true;
+  }
+
+  cc::BeginFrameAck ack(begin_frame_source_id, begin_frame_number,
+                        oldest_incorporated_frame_, 0, has_updates);
+  if (begin_frame_source_)
+    begin_frame_source_->DidFinishFrame(this, ack);
+}
+
+void RenderWidgetHostViewAura::OnBeginFrameDidNotDraw(cc::BeginFrameAck ack) {
+  // DelegatedFrameHost may have skipped the last frame(s).
+  ack.oldest_incorporated_frame = oldest_incorporated_frame_;
+  if (begin_frame_source_)
+    begin_frame_source_->DidFinishFrame(this, ack);
 }
 
 void RenderWidgetHostViewAura::ClearCompositorFrame() {