Splitting DidSwap in cc::SwapPromise into WillSwap and DidSwap

blimp/client/core/compositor/blimp_compositor.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "blimp/client/core/compositor/blimp_compositor.h"
 
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/histogram_macros.h"
@@ skipping 55 matching lines @@
       std::unique_ptr<cc::CopyOutputRequest> copy_request,
       base::WeakPtr<BlimpCompositor> compositor,
       scoped_refptr<base::SingleThreadTaskRunner> main_task_runner)
       : copy_request_(std::move(copy_request)),
         compositor_weak_ptr_(compositor),
         main_task_runner_(std::move(main_task_runner)) {}
   ~FrameTrackingSwapPromise() override = default;
 
   // cc::SwapPromise implementation.
   void DidActivate() override {}
-  void DidSwap(cc::CompositorFrameMetadata* metadata) override {
-    // DidSwap is called right before the CompositorFrame is submitted to the
-    // CompositorFrameSink, so we make sure to delay the copy request till that
-    // frame is submitted.
+  void WillSwap(cc::CompositorFrameMetadata* metadata) override {}
+  void DidSwap() override {
+    // DidSwap could be called on compositor thread and we need this to run on
+    // the main thread.
     main_task_runner_->PostTask(
         FROM_HERE,
         base::Bind(&BlimpCompositor::MakeCopyRequestOnNextSwap,
                    compositor_weak_ptr_, base::Passed(&copy_request_)));
   }
   DidNotSwapAction DidNotSwap(DidNotSwapReason reason) override {
     switch (reason) {
       case DidNotSwapReason::SWAP_FAILS:
         // The swap will fail if there is no frame damage, we can queue the
         // request right away.
@@ skipping 370 matching lines @@
   // Destroy the old LayerTreeHost state.
   host_.reset();
 
   // Cancel any outstanding CompositorFrameSink requests.  That way if we get an
   // async callback related to the old request we know to drop it.
   compositor_frame_sink_request_pending_ = false;
 }
 
 }  // namespace client
 }  // namespace blimp