Make OffscreenCanvas an EventTarget

third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp

Index: third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp
diff --git a/third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp b/third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp
index 72000926bf2f48aeef54bd80c41870358ee995d4..9ff34e4179bfa36edb4925ce2c0c7cb2bf3c18da 100644
--- a/third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp
+++ b/third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.cpp
@@ -5,6 +5,7 @@
 #include "modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.h"
 
 #include "bindings/modules/v8/OffscreenCanvasRenderingContext2DOrWebGLRenderingContextOrWebGL2RenderingContext.h"
+#include "core/dom/ExecutionContext.h"
 #include "core/frame/ImageBitmap.h"
 #include "core/frame/Settings.h"
 #include "core/workers/WorkerGlobalScope.h"
@@ -27,20 +28,23 @@ OffscreenCanvasRenderingContext2D::OffscreenCanvasRenderingContext2D(
     OffscreenCanvas* canvas,
     const CanvasContextCreationAttributes& attrs)
     : CanvasRenderingContext(nullptr, canvas, attrs) {
-  ExecutionContext* executionContext = scriptState->getExecutionContext();
-  if (executionContext->isDocument()) {
-    if (toDocument(executionContext)->settings()->disableReadingFromCanvas())
+  m_executionContext = scriptState->getExecutionContext();
+  if (m_executionContext.get()->isDocument()) {
+    if (toDocument(m_executionContext.get())
+            ->settings()
+            ->disableReadingFromCanvas())
       canvas->setDisableReadingFromCanvasTrue();
     return;
   }
 
   WorkerSettings* workerSettings =
-      toWorkerGlobalScope(executionContext)->workerSettings();
+      toWorkerGlobalScope(m_executionContext.get())->workerSettings();
   if (workerSettings && workerSettings->disableReadingFromCanvas())
     canvas->setDisableReadingFromCanvasTrue();
 }
 
 DEFINE_TRACE(OffscreenCanvasRenderingContext2D) {
+  visitor->trace(m_executionContext);
   CanvasRenderingContext::trace(visitor);
   BaseRenderingContext2D::trace(visitor);
 }