[cc] Pass on BeginFrameAcks from CompositorEBFS through RWHVAura, DFH.

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 1000c12f3f4f68d67ca1f1d5ad571e50f92963a4..89e0e002fb3fd5b7a60516bda4ae0384f82c0632 100644
--- a/content/browser/renderer_host/render_widget_host_view_aura.cc
+++ b/content/browser/renderer_host/render_widget_host_view_aura.cc
@@ -387,6 +387,8 @@ RenderWidgetHostViewAura::RenderWidgetHostViewAura(RenderWidgetHost* host,
       is_loading_(false),
       has_composition_text_(false),
       begin_frame_source_(nullptr),
+      latest_confirmed_begin_frame_sequence_number_(
+          cc::BeginFrameArgs::kInvalidFrameNumber),
       needs_begin_frames_(false),
       needs_flush_input_(false),
       added_frame_observer_(false),
@@ -675,8 +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) {
+    // Source changed, we don't know our freshness anymore.
+    latest_confirmed_begin_frame_sequence_number_ =
+        cc::BeginFrameArgs::kInvalidFrameNumber;
+  }
+
   needs_flush_input_ = false;
   host_->FlushInput();
   UpdateNeedsBeginFramesInternal();
@@ -950,6 +957,37 @@ void RenderWidgetHostViewAura::OnSwapCompositorFrame(
   }
   selection_controller_->OnSelectionBoundsChanged(selection.start,
                                                   selection.end);
+
+  cc::BeginFrameAck ack(frame.metadata.begin_frame_ack);
+  DCHECK_LE(cc::BeginFrameArgs::kStartingFrameNumber, ack.sequence_number);
+  // The CompositorFrame's damage was only incorporated if it wasn't skipped.
+  if (delegated_frame_host_->skipped_frames()) {
+    ack.has_damage = false;
+    ack.latest_confirmed_sequence_number =
+        latest_confirmed_begin_frame_sequence_number_;
+  } else {
+    DCHECK(ack.has_damage);
+    latest_confirmed_begin_frame_sequence_number_ =
+        ack.latest_confirmed_sequence_number;
+  }
+
+  if (begin_frame_source_)
+    begin_frame_source_->DidFinishFrame(this, ack);

[Eric Seckler, 2017/03/14 11:13:41]

+fsamuel, +brianderson:

Regarding the discussion about surface synchronization, here's what I think
might be a problem in the approach here:

DFH::SwapDelegatedFrame submits the CompositorFrame to the Surface(Factory),
where it may get stuck in pending state. DisplayScheduler won't see the surface
damage until it becomes active.

The BeginFrameAck, however, is sent separately (this LOC) so will be visible to
DisplayScheduler immediately. When we change DisplayScheduler to using these
acks for deciding when to draw&swap, it might try to draw&swap before the
pending CompositorFrame becomes active (i.e. before the damage is actually on
the surface corresponding to the BeginFrameAck).

Is that a problem?

[Fady Samuel, 2017/03/14 11:31:38]

Could we do this from Surface::ActivateFrame then, instead?

+}
+
+void RenderWidgetHostViewAura::OnBeginFrameDidNotDraw(
+    const cc::BeginFrameAck& ack) {
+  DCHECK_LE(cc::BeginFrameArgs::kStartingFrameNumber, ack.sequence_number);
+  DCHECK(!ack.has_damage);
+  cc::BeginFrameAck modified_ack = ack;
+  if (delegated_frame_host_->skipped_frames()) {
+    // If DelegatedFrameHost skipped the last frame(s), we need to wait for a
+    // newly submitted CompositorFrame before confirming newer sequence numbers.
+    modified_ack.latest_confirmed_sequence_number =
+        latest_confirmed_begin_frame_sequence_number_;
+  }
+  if (begin_frame_source_)
+    begin_frame_source_->DidFinishFrame(this, modified_ack);
 }
 
 void RenderWidgetHostViewAura::ClearCompositorFrame() {