GitLab

design doc:
https://docs.google.com/document/d/1O-fB83mrE0B_V8gzXNqHgmRLCvstTB4MMi3RnVLr8bE/edit#
https://docs.google.com/document/d/1obEb8K4mJpG9Y_x4_ZhvnbFHojZoLLzMCFsalkl8voc/edit#

This CL calls ImageResourceObserver::ImageNotifyFinished()
after SVG image loading is completed, not necessarily the same time as
ResourceLoader completion (e.g. DidFinishLoading()).
This makes SVG's <img> load event to be fired after SVG image loading
is completed even when the SVG has subresources loaded asynchronously.

1. Image::SetData() can return SizeAvailableAndLoadingAsynchronously
   when SVG image loading is not completed synchronously (due to
   subresources), and notifies the completion asynchronously via
   ImageObserver:LoadCompleted().
   LocalFrameClient::DispatchDidHandleOnloadEvents() is used as a
   notification of SVG image loading completion in SVGImage.

2. ImageResourceContent delays calling ImageNotifyFinished() and
   setting |content_status_| to kCached until SVG image loading is
   completed.

3. ImageLoader additionally delays the Document load event
   - from the first ImageChanged() during image loading
   - until (potentially delayed) ImageNotifyFinished().

In image loading not by ImageLoader, the Document load event is not
delayed from ResourceLoader completion until ImageNotifyFinished(),
but this is not a regression.

In image loading by ImageLoader, the Document load event is delayed
until ImageNotifyFinished() by the combination of
ResourceFetcher::loaders_ and ImageLoader.
ImageLoader starts delaying the Document load event
- Not from |image_| is set, because we shouldn't delay the Document
  load event when image loading is deferred.
- Not from ImageResourceContent::NotifyStartLoad(), to avoid additional
  ImageResourceObserver callbacks.

BUG=382170, 690480, 667641

Review-Url: https://codereview.chromium.org/2613853002
Cr-Commit-Position: refs/heads/master@{#472229}