Add header guards to CanvasAsyncBlobCreator.h

third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.h

Index: third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.h
diff --git a/third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.h b/third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.h
index ae4caa2dca5b73c677d48cec03c1b5f33d0ddc7b..a7f28c6a1cef17ff196991937b25431c4f409378 100644
--- a/third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.h
+++ b/third_party/WebKit/Source/core/html/canvas/CanvasAsyncBlobCreator.h
@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#ifndef CanvasAsyncBlobCreator_h
+#define CanvasAsyncBlobCreator_h
+
 #include "bindings/core/v8/ScriptPromiseResolver.h"
 #include "core/CoreExport.h"
 #include "core/dom/DOMTypedArray.h"
@@ -143,3 +146,5 @@ class CORE_EXPORT CanvasAsyncBlobCreator
 };
 
 }  // namespace blink
+
+#endif  // CanvasAsyncBlobCreator_h