cc: Introduce BeginFrame sequence numbers and acknowledgements.

content/browser/renderer_host/browser_compositor_view_mac.mm

Index: content/browser/renderer_host/browser_compositor_view_mac.mm
diff --git a/content/browser/renderer_host/browser_compositor_view_mac.mm b/content/browser/renderer_host/browser_compositor_view_mac.mm
index 93944dc85ad8f932bca73699111991cfd9af903f..4d54149f2d2c7286ff6295e9c482b9dbd1c37f71 100644
--- a/content/browser/renderer_host/browser_compositor_view_mac.mm
+++ b/content/browser/renderer_host/browser_compositor_view_mac.mm
@@ -279,8 +279,31 @@ void BrowserCompositorMac::SwapCompositorFrame(
     recyclable_compositor_->compositor()->SetScaleAndSize(scale_factor,
                                                           pixel_size);
   }
+  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));
+
+  // 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, has_updates,
+                        oldest_incorporated_frame_, 0);
+  if (begin_frame_source_)
+    begin_frame_source_->DidFinishFrame(this, ack);
+}
+
+void BrowserCompositorMac::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 BrowserCompositorMac::SetHasTransparentBackground(bool transparent) {
@@ -460,6 +483,12 @@ bool BrowserCompositorMac::IsAutoResizeEnabled() const {
 // cc::BeginFrameSourceBase, public:
 
 void BrowserCompositorMac::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;
+  }
+
   client_->BrowserCompositorMacSendBeginFrame(args);
   last_begin_frame_args_ = args;
 }