cc: Fix DCHECK failure for pending tree raster duration timer.

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 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 "cc/trees/layer_tree_host_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 2098 matching lines @@
 
 void LayerTreeHostImpl::ActivateSyncTree() {
   if (pending_tree_) {
     TRACE_EVENT_ASYNC_END0("cc", "PendingTree:waiting", pending_tree_.get());
     active_tree_->lifecycle().AdvanceTo(LayerTreeLifecycle::kBeginningSync);
 
     DCHECK(pending_tree_duration_timer_);
     // Reset will call the destructor and log the timer histogram.
     pending_tree_duration_timer_.reset();
 
+    // In most cases, this will be reset in NotifyReadyToActivate, since we
+    // activate the pending tree only when its ready. But an activation may be
+    // forced, in the case of a context loss for instance, so reset it here as
+    // well.
+    pending_tree_raster_duration_timer_.reset();
+
     // Process any requests in the UI resource queue.  The request queue is
     // given in LayerTreeHost::FinishCommitOnImplThread.  This must take place
     // before the swap.
     pending_tree_->ProcessUIResourceRequestQueue();
 
     if (pending_tree_->needs_full_tree_sync()) {
       TreeSynchronizer::SynchronizeTrees(pending_tree_.get(),
                                          active_tree_.get());
     }
 
@@ skipping 2192 matching lines @@
 
 void LayerTreeHostImpl::ShowScrollbarsForImplScroll(ElementId element_id) {
   if (!element_id)
     return;
   if (ScrollbarAnimationController* animation_controller =
           ScrollbarAnimationControllerForElementId(element_id))
     animation_controller->DidScrollUpdate();
 }
 
 }  // namespace cc