Oilpan: move 2D Canvas and WebGL objects to the heap.

Source/core/html/canvas/WebGLSharedObject.cpp

Index: Source/core/html/canvas/WebGLSharedObject.cpp
diff --git a/Source/core/html/canvas/WebGLSharedObject.cpp b/Source/core/html/canvas/WebGLSharedObject.cpp
index 32f4595c670ad923c1da3d21972aacdf1cb42392..8bc19749efb87dee34e6852c6db5a6567e826007 100644
--- a/Source/core/html/canvas/WebGLSharedObject.cpp
+++ b/Source/core/html/canvas/WebGLSharedObject.cpp
@@ -50,7 +50,7 @@ void WebGLSharedObject::detachContextGroup()
     if (m_contextGroup) {
         deleteObject(0);
         m_contextGroup->removeObject(this);
-        m_contextGroup = 0;
+        m_contextGroup = nullptr;
     }
 }