Replace AllowCrossThreadAccess() + GCed pointers with wrapCrossThreadPersistent()

third_party/WebKit/Source/core/imagebitmap/ImageBitmapFactories.cpp

Index: third_party/WebKit/Source/core/imagebitmap/ImageBitmapFactories.cpp
diff --git a/third_party/WebKit/Source/core/imagebitmap/ImageBitmapFactories.cpp b/third_party/WebKit/Source/core/imagebitmap/ImageBitmapFactories.cpp
index 9c29fa204ffb11267ec57714fdc84336fb9bdcbc..86b14a70ef21f6209b91835456ba85c93325f7a7 100644
--- a/third_party/WebKit/Source/core/imagebitmap/ImageBitmapFactories.cpp
+++ b/third_party/WebKit/Source/core/imagebitmap/ImageBitmapFactories.cpp
@@ -220,7 +220,7 @@ void ImageBitmapFactories::ImageBitmapLoader::scheduleAsyncImageBitmapDecoding(D
     if (arrayBuffer->byteLength() >= longTaskByteLengthThreshold)
         taskSize = BackgroundTaskRunner::TaskSizeLongRunningTask;
     WebTaskRunner* taskRunner = Platform::current()->currentThread()->getWebTaskRunner();
-    BackgroundTaskRunner::postOnBackgroundThread(BLINK_FROM_HERE, threadSafeBind(&ImageBitmapFactories::ImageBitmapLoader::decodeImageOnDecoderThread, AllowCrossThreadAccess(this), AllowCrossThreadAccess(taskRunner), AllowCrossThreadAccess(arrayBuffer)), taskSize);
+    BackgroundTaskRunner::postOnBackgroundThread(BLINK_FROM_HERE, threadSafeBind(&ImageBitmapFactories::ImageBitmapLoader::decodeImageOnDecoderThread, wrapCrossThreadPersistent(this), AllowCrossThreadAccess(taskRunner), wrapCrossThreadPersistent(arrayBuffer)), taskSize);

[sof, 2016/05/17 05:44:46]

Clarifying Q: why is it considered preferable to have the user/developer know
who manages the argument pointer being passed, and choose
wrapCrossThreadPersistent() / AllowCrossThreadAccess() accordingly?

[hiroshige, 2016/05/17 05:57:12]

|AllowCrossThreadAccess(taskRunner)| will be replaced by
|crossThreadUnretained(taskRunner)|.

This is to make retainedness of bound arguments explicit.
Binding CrossThreadPersistent clearly retains strong reference, while
crossThreadUnretained() means WTF::Function doesn't retain strong reference nor
ownership.

Previously, AllowCrossThreadAccess(pointerToGCedObject) retains strong reference
while AllowCrossThreadAccess(pointerToNONGCedObject) does NOT retain strong
reference/ownership.
Issue 597856 is cleaning up such confusing cases.

[sof, 2016/05/17 06:05:24]

ok, we'll arrive at names that work better iteratively possibly -- having to be
explicit about something be Persistent-backed (in whatever variant) seems like
an implementation detail escaping too far out.

 }
 
 void ImageBitmapFactories::ImageBitmapLoader::decodeImageOnDecoderThread(WebTaskRunner* taskRunner, DOMArrayBuffer* arrayBuffer)
@@ -240,7 +240,7 @@ void ImageBitmapFactories::ImageBitmapLoader::decodeImageOnDecoderThread(WebTask
         decoder->setData(sharedBuffer.get(), true);
         frame = ImageBitmap::getSkImageFromDecoder(std::move(decoder));
     }
-    taskRunner->postTask(BLINK_FROM_HERE, threadSafeBind(&ImageBitmapFactories::ImageBitmapLoader::resolvePromiseOnOriginalThread, AllowCrossThreadAccess(this), frame.release()));
+    taskRunner->postTask(BLINK_FROM_HERE, threadSafeBind(&ImageBitmapFactories::ImageBitmapLoader::resolvePromiseOnOriginalThread, wrapCrossThreadPersistent(this), frame.release()));
 }
 
 void ImageBitmapFactories::ImageBitmapLoader::resolvePromiseOnOriginalThread(PassRefPtr<SkImage> frame)