cc: Only allow trees created at the current viewport size to draw.

cc/thread_proxy.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/thread_proxy.h"
 
 #include "base/auto_reset.h"
 #include "base/bind.h"
 #include "base/debug/trace_event.h"
 #include "cc/delay_based_time_source.h"
@@ skipping 1158 matching lines @@
                 smoothnessTakesPriorityExpirationDelay * 1000);
     }
 
     // We use the same priority for both trees by default.
     TreePriority priority = SAME_PRIORITY_FOR_BOTH_TREES;
 
     // Smoothness takes priority if expiration time is in the future.
     if (m_smoothnessTakesPriorityExpirationTime > base::TimeTicks::Now())
         priority = SMOOTHNESS_TAKES_PRIORITY;
 
-    // New content always takes priority when we have an active tree with
-    // evicted resources.
-    if (m_layerTreeHostImpl->activeTree()->ContentsTexturesPurged())
+    // New content always takes priority when the active tree has
+    // evicted resources or there is an invalid viewport size.
+    if (m_layerTreeHostImpl->activeTree()->ContentsTexturesPurged() ||
+        m_layerTreeHostImpl->activeTree()->ViewportSizeInvalid())
         priority = NEW_CONTENT_TAKES_PRIORITY;
 
     m_layerTreeHostImpl->setTreePriority(priority);
 
     // Notify the the client of this compositor via the output surface.
     // TODO(epenner): Route this to compositor-thread instead of output-surface
     // after GTFO refactor of compositor-thread (http://crbug/170828).
     if (m_layerTreeHostImpl->outputSurface()) {
         m_layerTreeHostImpl->outputSurface()->UpdateSmoothnessTakesPriority(
             priority == SMOOTHNESS_TAKES_PRIORITY);
@@ skipping 19 matching lines @@
 
 void ThreadProxy::renewTreePriorityOnImplThread()
 {
     DCHECK(m_renewTreePriorityOnImplThreadPending);
     m_renewTreePriorityOnImplThreadPending = false;
 
     renewTreePriority();
 }
 
 }  // namespace cc