Revert of Disallow users modify canvas after it transfers control to offscreen

third_party/WebKit/Source/modules/canvas/HTMLCanvasElementModule.idl

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // https://html.spec.whatwg.org/#the-canvas-element
 
 typedef (CanvasRenderingContext2D or
          WebGLRenderingContext or
          WebGL2RenderingContext or
          ImageBitmapRenderingContext) RenderingContext;
 
 partial interface HTMLCanvasElement
 {
     // The PermissiveDictionaryConversion extended attribute is needed to allow the
     // autogenerated code to match the behavior of the custom binding. Web IDL
     // requires throwing TypeError if the incoming argument is not an object type
     // (and is not undefined or null). The binding must ignore this.
     // Related spec issue: https://github.com/whatwg/html/issues/595
-    [RaisesException] RenderingContext? getContext(DOMString contextId, [PermissiveDictionaryConversion] optional CanvasContextCreationAttributes attributes);
+    RenderingContext? getContext(DOMString contextId, [PermissiveDictionaryConversion] optional CanvasContextCreationAttributes attributes);
     [RuntimeEnabled=ExperimentalCanvasFeatures, RaisesException] OffscreenCanvas transferControlToOffscreen();
 };