Implicit prefinalizer registration.

third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp

Index: third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp b/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
index b90acddd296bc82cb1aae752286133a96ea39cef..5b164dee0321e3a1ac483a757ea000ecf42945f8 100644
--- a/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
@@ -146,7 +146,8 @@ HTMLCanvasElement::~HTMLCanvasElement() {
 }
 
 void HTMLCanvasElement::dispose() {
-  releasePlaceholderFrame();
+  if (placeholderFrame())
+    releasePlaceholderFrame();
 
   if (m_context) {
     m_context->detachCanvas();