Make WebView::close not crash and start to fix navigation in SkyShell

sky/shell/ui/animator.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 "sky/shell/ui/animator.h"
 
 #include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 
 namespace sky {
@@ skipping 16 matching lines @@
   engine_requested_frame_ = true;
 
   if (!frame_in_progress_) {
     frame_in_progress_ = true;
     base::MessageLoop::current()->PostTask(
         FROM_HERE,
         base::Bind(&Animator::BeginFrame, weak_factory_.GetWeakPtr()));
   }
 }
 
+void Animator::CancelFrameRequest() {
+  engine_requested_frame_ = false;
+}
+
 void Animator::BeginFrame() {
   DCHECK(frame_in_progress_);
-  DCHECK(engine_requested_frame_);
+  // There could be a request in the message loop at time of cancel.
+  if (!engine_requested_frame_) {
+    frame_in_progress_ = false;
+    return;
+  }
   engine_requested_frame_ = false;
 
   engine_->BeginFrame(base::TimeTicks::Now());
   config_.gpu_task_runner->PostTaskAndReply(
       FROM_HERE,
       base::Bind(&GPUDelegate::Draw, config_.gpu_delegate, engine_->Paint()),
       base::Bind(&Animator::OnFrameComplete, weak_factory_.GetWeakPtr()));
 }
 
 void Animator::OnFrameComplete() {
   DCHECK(frame_in_progress_);
   frame_in_progress_ = false;
   if (engine_requested_frame_) {
     frame_in_progress_ = true;
     BeginFrame();
   }
 }
 
 }  // namespace shell
 }  // namespace sky