WebView: Make draws asynchronous during fling and tick on renderer side

Tick fling animations at the beginning of the frame, on the renderer
side. This is done by calling OnComputeScroll directly from
SynchronousCompositorProxy::OnBeginFrame rather than sending the ipc
message from the browser side. However, we have to send the ipc once,
since we shouldn't tick fling animations if a view has overridden
OnComputeScroll.

Previously, draws after calls to OnComputeScroll were synchronous so
that child views would scroll with the webview. This change makes draws
after OnComputeScroll asynchronous and ticks fling animations during
BeginFrame.

Bug: 801759
Change-Id: Iaf95ecc44586ae212630602b38b3ab570b27132b
Reviewed-on: https://chromium-review.googlesource.com/894176
Commit-Queue: James Wallace-Lee <jamwalla@chromium.org>
Reviewed-by: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537375}

content/renderer/android/synchronous_compositor_proxy.cc

@@ -36,6 +36,10 @@ SynchronousCompositorProxy::SynchronousCompositorProxy(
       hardware_draw_reply_(nullptr),
       software_draw_reply_(nullptr),
       hardware_draw_reply_async_(false),
+      compute_scroll_called_via_ipc_(false),
+      browser_needs_begin_frame_state_(false),
+      needs_begin_frame_for_frame_sink_(false),
+      needs_begin_frame_for_animate_input_(false),
       version_(0u),
       page_scale_factor_(0.f),
       min_page_scale_factor_(0.f),
@@ -69,8 +73,13 @@ void SynchronousCompositorProxy::SetLayerTreeFrameSink(
 }
 
 void SynchronousCompositorProxy::SetNeedsSynchronousAnimateInput() {
-  need_animate_scroll_ = true;
-  Invalidate();
+  if (compute_scroll_called_via_ipc_) {
+    needs_begin_frame_for_animate_input_ = true;
+    SendSetNeedsBeginFramesIfNeeded();
+  } else {
+    need_animate_scroll_ = true;
+    Invalidate();
+  }
 }
 
 void SynchronousCompositorProxy::UpdateRootLayerState(
@@ -124,9 +133,10 @@ void SynchronousCompositorProxy::PopulateCommonParams(
   params->page_scale_factor = page_scale_factor_;
   params->min_page_scale_factor = min_page_scale_factor_;
   params->max_page_scale_factor = max_page_scale_factor_;
-  params->need_animate_scroll = need_animate_scroll_;
   params->need_invalidate_count = need_invalidate_count_;
   params->did_activate_pending_tree_count = did_activate_pending_tree_count_;
+  if (!compute_scroll_called_via_ipc_)
+    params->need_animate_scroll = need_animate_scroll_;
 }
 
 void SynchronousCompositorProxy::OnMessageReceived(
@@ -360,13 +370,24 @@ void SynchronousCompositorProxy::SubmitCompositorFrame(
   }
 }
 
+void SynchronousCompositorProxy::SendSetNeedsBeginFramesIfNeeded() {
+  bool needs_begin_frames =
+      needs_begin_frame_for_frame_sink_ || needs_begin_frame_for_animate_input_;
+  if (browser_needs_begin_frame_state_ != needs_begin_frames)
+    Send(new SyncCompositorHostMsg_SetNeedsBeginFrames(routing_id_,
+                                                       needs_begin_frames));
+  browser_needs_begin_frame_state_ = needs_begin_frames;
+}
+
 void SynchronousCompositorProxy::SetNeedsBeginFrames(bool needs_begin_frames) {
-  Send(new SyncCompositorHostMsg_SetNeedsBeginFrames(routing_id_,
-                                                     needs_begin_frames));
+  needs_begin_frame_for_frame_sink_ = needs_begin_frames;
+  SendSetNeedsBeginFramesIfNeeded();
 }
 
 void SynchronousCompositorProxy::OnComputeScroll(
     base::TimeTicks animation_time) {
+  compute_scroll_called_via_ipc_ = true;
+
   if (need_animate_scroll_) {
     need_animate_scroll_ = false;
     input_handler_proxy_->SynchronouslyAnimate(animation_time);
@@ -380,7 +401,11 @@ void SynchronousCompositorProxy::OnSetBeginFrameSourcePaused(bool paused) {
 }
 
 void SynchronousCompositorProxy::OnBeginFrame(const viz::BeginFrameArgs& args) {
-  if (layer_tree_frame_sink_)
+  if (needs_begin_frame_for_animate_input_) {
+    needs_begin_frame_for_animate_input_ = false;
+    input_handler_proxy_->SynchronouslyAnimate(args.frame_time);
+  }
+  if (needs_begin_frame_for_frame_sink_ && layer_tree_frame_sink_)
     layer_tree_frame_sink_->BeginFrame(args);
 
   SyncCompositorCommonRendererParams param;

content/renderer/android/synchronous_compositor_proxy.h

@@ -67,6 +67,8 @@ class SynchronousCompositorProxy : public ui::SynchronousInputHandler,
  private:
   struct SharedMemoryWithSize;
 
+  void SendSetNeedsBeginFramesIfNeeded();
+
   // IPC handlers.
   void OnComputeScroll(base::TimeTicks animation_time);
   void OnSetBeginFrameSourcePaused(bool paused);
@@ -116,6 +118,11 @@ class SynchronousCompositorProxy : public ui::SynchronousInputHandler,
   bool hardware_draw_reply_async_;
   bool begin_frame_paused_ = false;
 
+  bool compute_scroll_called_via_ipc_;
+  bool browser_needs_begin_frame_state_;
+  bool needs_begin_frame_for_frame_sink_;
+  bool needs_begin_frame_for_animate_input_;
+
   // From browser.
   std::unique_ptr<SharedMemoryWithSize> software_draw_shm_;