Allocate OverlapMapContainers in vector rather than on stack with copy

third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp

Index: third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
index 343d31601d4c069357d9a39c60ff0740988c0d92..f4993f7b3402408b3e4a75628ec8fca177d7b546 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
@@ -118,7 +118,7 @@ class CompositingRequirementsUpdater::OverlapMap {
     // This effectively creates a new "clean slate" for overlap state.
     // This is used when we know that a subtree or remaining set of
     // siblings does not need to check overlap with things behind it.
-    m_overlapStack.append(OverlapMapContainers());
+    m_overlapStack.grow(m_overlapStack.size() + 1);
   }
 
   void finishCurrentOverlapTestingContext() {