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

cc/layer_tree_host_impl.cc

Index: cc/layer_tree_host_impl.cc
diff --git a/cc/layer_tree_host_impl.cc b/cc/layer_tree_host_impl.cc
index 06db701f3a9279b63d86d5ec7fdfe06c9e84883a..4d2bc9a52a2523eca4cabec4f76d0326ead612d7 100644
--- a/cc/layer_tree_host_impl.cc
+++ b/cc/layer_tree_host_impl.cc
@@ -234,6 +234,10 @@ bool LayerTreeHostImpl::canDraw()
         TRACE_EVENT_INSTANT0("cc", "LayerTreeHostImpl::canDraw empty viewport");
         return false;
     }
+    if (m_activeTree->ViewportSizeInvalid()) {
+        TRACE_EVENT_INSTANT0("cc", "LayerTreeHostImpl::canDraw viewport size recently changed");
+        return false;
+    }
     if (!m_renderer) {
         TRACE_EVENT_INSTANT0("cc", "LayerTreeHostImpl::canDraw no renderer");
         return false;
@@ -1102,6 +1106,9 @@ void LayerTreeHostImpl::setViewportSize(const gfx::Size& layoutViewportSize, con
     if (layoutViewportSize == m_layoutViewportSize && deviceViewportSize == m_deviceViewportSize)
         return;
 
+    if (pendingTree() && m_deviceViewportSize != deviceViewportSize)
+        activeTree()->SetViewportSizeInvalid();
+
     m_layoutViewportSize = layoutViewportSize;
     m_deviceViewportSize = deviceViewportSize;