[Android] Speculative fix for crash during overscroll effect creation

content/browser/renderer_host/render_widget_host_view_android.cc

 // Copyright (c) 2012 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 "content/browser/renderer_host/render_widget_host_view_android.h"
 
 #include <android/bitmap.h>
 
 #include "base/android/build_info.h"
 #include "base/basictypes.h"
@@ skipping 1583 matching lines @@
     content_view_core_->DidStopFlinging();
 }
 
 void RenderWidgetHostViewAndroid::SetContentViewCore(
     ContentViewCoreImpl* content_view_core) {
   RemoveLayers();
   StopObservingRootWindow();
 
   bool resize = false;
   if (content_view_core != content_view_core_) {
+    overscroll_effect_.reset();
     selection_controller_.reset();
     ReleaseLocksOnSurface();
     resize = true;
   }
 
   content_view_core_ = content_view_core;
 
   BrowserAccessibilityManager* manager = NULL;
   if (host_)
     manager = host_->GetRootBrowserAccessibilityManager();
@@ skipping 10 matching lines @@
     return;
 
   StartObservingRootWindow();
 
   if (resize)
     WasResized();
 
   if (!selection_controller_)
     selection_controller_.reset(new TouchSelectionController(this));
 
-  if (!content_view_core_)
-    overscroll_effect_.reset();
-  else if (overscroll_effect_enabled_ && !overscroll_effect_)
+  if (overscroll_effect_enabled_ && !overscroll_effect_ &&
+      content_view_core_->GetWindowAndroid()->GetCompositor())
     overscroll_effect_ = CreateOverscrollEffect(content_view_core_);
 }
 
 void RenderWidgetHostViewAndroid::RunAckCallbacks() {
   while (!ack_callbacks_.empty()) {
     ack_callbacks_.front().Run();
     ack_callbacks_.pop();
   }
 }
 
 void RenderWidgetHostViewAndroid::OnGestureEvent(
     const ui::GestureEventData& gesture) {
   if (gesture_text_selector_.OnGestureEvent(gesture))
     return;
 
   SendGestureEvent(CreateWebGestureEventFromGestureEventData(gesture));
 }
 
 void RenderWidgetHostViewAndroid::OnCompositingDidCommit() {
   RunAckCallbacks();
 }
 
+
+void RenderWidgetHostViewAndroid::OnAttachCompositor() {

[no sievers, 2014/08/25 21:48:52]

I just realized that these callbacks are a bit flaky anyways, since we call
RemoveObserver() when the view is hidden.

+  DCHECK(content_view_core_);
+  if (overscroll_effect_enabled_)
+    overscroll_effect_ = CreateOverscrollEffect(content_view_core_);
+}
+
 void RenderWidgetHostViewAndroid::OnDetachCompositor() {
   DCHECK(content_view_core_);
   DCHECK(!using_synchronous_compositor_);
   RunAckCallbacks();
+  overscroll_effect_.reset();
 }
 
 void RenderWidgetHostViewAndroid::OnVSync(base::TimeTicks frame_time,
                                           base::TimeDelta vsync_period) {
   TRACE_EVENT0("cc", "RenderWidgetHostViewAndroid::OnVSync");
   if (!host_)
     return;
 
   const uint32 current_vsync_requests = outstanding_vsync_requests_;
   outstanding_vsync_requests_ = 0;
@@ skipping 156 matching lines @@
   results->orientationAngle = display.RotationAsDegree();
   results->orientationType =
       RenderWidgetHostViewBase::GetOrientationTypeForMobile(display);
   gfx::DeviceDisplayInfo info;
   results->depth = info.GetBitsPerPixel();
   results->depthPerComponent = info.GetBitsPerComponent();
   results->isMonochrome = (results->depthPerComponent == 0);
 }
 
 } // namespace content