Add thread affinity and ASSERT() for same-thread restriction to WTF::Function

third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h

Index: third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h
diff --git a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h
index 327b27e7277a09a397ab4cf5c74a90b2723d4a11..5ea2af0890567d4a1b4e16696827b2a5b2453c1b 100644
--- a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h
+++ b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h
@@ -170,7 +170,7 @@ public:
     // Otherwise, bind to the default FBO.
     void restoreFramebufferBindings();
 
-    void addNewMailboxCallback(PassOwnPtr<Closure> closure) { m_newMailboxCallback = std::move(closure); }
+    void addNewMailboxCallback(PassOwnPtr<SameThreadClosure> closure) { m_newMailboxCallback = std::move(closure); }
 
 protected: // For unittests
     DrawingBuffer(
@@ -313,7 +313,7 @@ private:
     };
     FrontBufferInfo m_frontColorBuffer;
 
-    OwnPtr<Closure> m_newMailboxCallback;
+    OwnPtr<SameThreadClosure> m_newMailboxCallback;
 
     // This is used when the user requests either a depth or stencil buffer.
     Platform3DObject m_depthStencilBuffer;