Introduce Document::unthrottledTaskRunner()

third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp

 /*
  * Copyright (C) 2004, 2006, 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 662 matching lines @@
 
 void HTMLCanvasElement::toBlob(BlobCallback* callback, const String& mimeType, const ScriptValue& qualityArgument, ExceptionState& exceptionState)
 {
     if (!originClean()) {
         exceptionState.throwSecurityError("Tainted canvases may not be exported.");
         return;
     }
 
     if (!isPaintable()) {
         // If the canvas element's bitmap has no pixels
-        Platform::current()->mainThread()->getWebTaskRunner()->postTask(BLINK_FROM_HERE, WTF::bind(&BlobCallback::handleEvent, wrapPersistent(callback), nullptr));
+        document().unthrottledTaskRunner()->postTask(BLINK_FROM_HERE, WTF::bind(&BlobCallback::handleEvent, wrapPersistent(callback), nullptr));

[Sami, 2016/07/08 09:13:29]

Looks like this can execute script. I wonder if it should be throttled or not?
It wasn't throttled before so you're not really changing anything, but we should
think about whether we need another task runner for things like these (or if we
should just reuse the timer task runner).

[dcheng, 2016/07/08 10:27:37]

What are "things like these"?

To me, the distinction between loading and non-loading tasks is pretty clear, so
a loading task runner makes sense.

The distinction between timer and unthrottled tasks is also clear, so those task
runners make sense.

I'm having trouble understanding what category a fourth task runner would
fulfill though.

         return;
     }
 
     double startTime = WTF::monotonicallyIncreasingTime();
     double quality = UndefinedQualityValue;
     if (!qualityArgument.isEmpty()) {
         v8::Local<v8::Value> v8Value = qualityArgument.v8Value();
         if (v8Value->IsNumber()) {
             quality = v8Value.As<v8::Number>()->Value();
         }
@@ skipping 500 matching lines @@
 
 bool HTMLCanvasElement::createSurfaceLayer()
 {
     DCHECK(!m_surfaceLayerBridge);
     std::unique_ptr<CanvasSurfaceLayerBridgeClient> bridgeClient = wrapUnique(new CanvasSurfaceLayerBridgeClientImpl());
     m_surfaceLayerBridge = wrapUnique(new CanvasSurfaceLayerBridge(std::move(bridgeClient)));
     return m_surfaceLayerBridge->createSurfaceLayer(this->width(), this->height());
 }
 
 } // namespace blink