Introduce Document::unthrottledTaskRunner()

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

Index: third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp b/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
index c4f61a920737688205b7a09ae86f9296d2369585..e3dda03b6dd9e0343a1519ace974bb1eb50a5dc4 100644
--- a/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
@@ -680,7 +680,7 @@ void HTMLCanvasElement::toBlob(BlobCallback* callback, const String& mimeType, c
 
     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;
     }