Add rendering context and rendering 2D context to OffscreenCanvas

third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvas.idl

Index: third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvas.idl
diff --git a/third_party/WebKit/Source/core/html/canvas/OffscreenCanvas.idl b/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvas.idl
similarity index 59%
rename from third_party/WebKit/Source/core/html/canvas/OffscreenCanvas.idl
rename to third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvas.idl
index be5bf9128569e7bf0702354f142c44a037338a56..b1436b0a5c5f0442a648cbee0435fa5b037d9016 100644
--- a/third_party/WebKit/Source/core/html/canvas/OffscreenCanvas.idl
+++ b/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvas.idl
@@ -2,6 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// Note: If there're more context types implemented, they should be added here
+// to form a union type of OffscreenCanvasRenderingContext
+typedef OffscreenCanvasRenderingContext2D OffscreenRenderingContext;
+
 [
     Constructor([EnforceRange] unsigned long width, [EnforceRange] unsigned long height),
     GarbageCollected,
@@ -10,4 +14,6 @@
 ] interface OffscreenCanvas {
     [EnforceRange] attribute unsigned long width;
     [EnforceRange] attribute unsigned long height;
+
+    OffscreenRenderingContext? getContext(DOMString contextId, optional CanvasContextCreationAttributes attributes); 
 };