Splitting DidSwap in cc::SwapPromise into WillSwap and DidSwap

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index de50e70ea351370c82a80dde3788be6b893962c6..4aa714074ce6f7b299b87be9c3123b5d4da58df3 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1666,6 +1666,10 @@ bool LayerTreeHostImpl::DrawLayers(FrameData* frame) {
   compositor_frame.render_pass_list = std::move(frame->render_passes);
   compositor_frame_sink_->SubmitCompositorFrame(std::move(compositor_frame));
 
+  // Clears the list of swap promises after calling DidSwap on each of them to
+  // signal that the swap is over.
+  active_tree()->ClearSwapPromises();
+
   // The next frame should start by assuming nothing has changed, and changes
   // are noted as they occur.
   // TODO(boliu): If we did a temporary software renderer frame, propogate the