Replace AllowCrossThreadAccess() + GCed pointers with wrapCrossThreadPersistent()

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

 /*
  * Copyright (c) 2013, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 202 matching lines @@
 void ImageBitmapFactories::ImageBitmapLoader::scheduleAsyncImageBitmapDecoding(DOMArrayBuffer* arrayBuffer)
 {
     // For a 4000*4000 png image where each 10*10 tile is filled in by a random RGBA value,
     // the byteLength is around 2M, and it typically takes around 4.5ms to decode on a
     // current model of Linux desktop.
     const int longTaskByteLengthThreshold = 2000000;
     BackgroundTaskRunner::TaskSize taskSize = BackgroundTaskRunner::TaskSizeShortRunningTask;
     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)
 {
     ASSERT(!isMainThread());
     RefPtr<SharedBuffer> sharedBuffer = SharedBuffer::create(static_cast<char*>(arrayBuffer->data()), static_cast<size_t>(arrayBuffer->byteLength()));
 
     ImageDecoder::AlphaOption alphaOp = ImageDecoder::AlphaPremultiplied;
     if (m_options.premultiplyAlpha() == "none")
         alphaOp = ImageDecoder::AlphaNotPremultiplied;
     ImageDecoder::GammaAndColorProfileOption colorSpaceOp = ImageDecoder::GammaAndColorProfileApplied;
     if (m_options.colorSpaceConversion() == "none")
         colorSpaceOp = ImageDecoder::GammaAndColorProfileIgnored;
     OwnPtr<ImageDecoder> decoder(ImageDecoder::create(*sharedBuffer, alphaOp, colorSpaceOp));
     RefPtr<SkImage> frame;
     if (decoder) {
         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)
 {
     if (!frame) {
         rejectPromise();
         return;
     }
     ASSERT(frame->width() && frame->height());
 
@@ skipping 14 matching lines @@
     m_factory->didFinishLoading(this);
 }
 
 DEFINE_TRACE(ImageBitmapFactories::ImageBitmapLoader)
 {
     visitor->trace(m_factory);
     visitor->trace(m_resolver);
 }
 
 } // namespace blink