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..20b50133b69a7b69dbf79ed7db510249a5ee3f65 100644
--- a/content/browser/renderer_host/browser_compositor_view_mac.mm
+++ b/content/browser/renderer_host/browser_compositor_view_mac.mm
@@ -279,8 +279,33 @@ 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 latest_confirmed_frame = frame.metadata.latest_confirmed_frame;
+
   delegated_frame_host_->SwapDelegatedFrame(compositor_frame_sink_id,
                                             std::move(frame));
+
+  // The CompositorFrame's damage was only incorporated if it wasn't skipped.
+  bool has_damage = false;
+  if (!delegated_frame_host_->skipped_frames()) {
+    latest_confirmed_frame_ = latest_confirmed_frame;
+    has_damage = true;
+  }
+
+  cc::BeginFrameAck ack(begin_frame_source_id, begin_frame_number,
+                        latest_confirmed_frame_, 0, has_damage);
+  if (begin_frame_source_)
+    begin_frame_source_->DidFinishFrame(this, ack);
+}
+
+void BrowserCompositorMac::OnBeginFrameDidNotDraw(
+    const cc::BeginFrameAck& ack) {
+  // DelegatedFrameHost may have skipped the last frame(s).
+  cc::BeginFrameAck modified_ack = ack;
+  modified_ack.latest_confirmed_frame = latest_confirmed_frame_;
+  if (begin_frame_source_)
+    begin_frame_source_->DidFinishFrame(this, modified_ack);
 }
 
 void BrowserCompositorMac::SetHasTransparentBackground(bool transparent) {
@@ -460,6 +485,12 @@ 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.
+    DCHECK_LT(cc::BeginFrameArgs::kInvalidFrameNumber, args.sequence_number);
+    latest_confirmed_frame_ = args.sequence_number - 1;
+  }
+
   client_->BrowserCompositorMacSendBeginFrame(args);
   last_begin_frame_args_ = args;
 }