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

cc/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/layer_tree_host_impl.h"
 
 #include <algorithm>
 
 #include "base/basictypes.h"
 #include "base/debug/trace_event.h"
@@ skipping 205 matching lines @@
     // in the proper places and update the notifyIfCanDrawChanged test.
 
     if (!rootLayer()) {
         TRACE_EVENT_INSTANT0("cc", "LayerTreeHostImpl::canDraw no root layer");
         return false;
     }
     if (deviceViewportSize().IsEmpty()) {
         TRACE_EVENT_INSTANT0("cc", "LayerTreeHostImpl::canDraw empty viewport");
         return false;
     }
+    if (deviceViewportSize() != activeTree()->device_viewport_size()) {
+        TRACE_EVENT_INSTANT0("cc", "LayerTreeHostImpl::canDraw viewport resize incomplete");
+        return false;
+    }
     if (!m_renderer) {
         TRACE_EVENT_INSTANT0("cc", "LayerTreeHostImpl::canDraw no renderer");
         return false;
     }
     if (m_activeTree->ContentsTexturesPurged()) {
         TRACE_EVENT_INSTANT0("cc", "LayerTreeHostImpl::canDraw contents textures purged");
         return false;
     }
     return true;
 }
@@ skipping 850 matching lines @@
 
     return true;
 }
 
 void LayerTreeHostImpl::setViewportSize(const gfx::Size& layoutViewportSize, const gfx::Size& deviceViewportSize)
 {
     if (layoutViewportSize == m_layoutViewportSize && deviceViewportSize == m_deviceViewportSize)
         return;
 
     m_layoutViewportSize = layoutViewportSize;
     m_deviceViewportSize = deviceViewportSize;

[danakj, 2013/02/13 05:44:30]

Can you just remove the m_deviceViewportSize from the host then? It's just
duplicating the value on the pending tree now, no?

In fact can you move both viewport sizes to the trees? Seems like this whole
function is redundant with what happens in the LTImpl.

 
+    if (m_settings.implSidePainting)
+        pendingTree()->SetDeviceViewportSize(deviceViewportSize);
+    else
+        activeTree()->SetDeviceViewportSize(deviceViewportSize);
+
     updateMaxScrollOffset();
 
     if (m_renderer)
         m_renderer->viewportChanged();

[danakj, 2013/02/13 05:44:30]

You want this to happen when the active tree's viewport changes, right? Should
move this to LTImpl and do that?

 
     m_client->onCanDrawStateChanged(canDraw());
 }
 
 static void adjustScrollsForPageScaleChange(LayerImpl* layerImpl, float pageScaleChange)
 {
     if (!layerImpl)
         return;
 
     if (layerImpl->scrollable()) {
@@ skipping 616 matching lines @@
     if (m_tileManager)
         m_tileManager->SetRecordRenderingStats(m_debugState.recordRenderingStats());
 }
 
 void LayerTreeHostImpl::savePaintTime(const base::TimeDelta& totalPaintTime)
 {
     m_paintTimeCounter->SavePaintTime(totalPaintTime);
 }
 
 }  // namespace cc