Phase III Step 2: Call imageNotifyFinished() and image load event after SVG loading completes

third_party/WebKit/Source/core/loader/resource/ImageResource.cpp

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller (mueller@kde.org)
     Copyright (C) 2002 Waldo Bastian (bastian@kde.org)
     Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
     Copyright (C) 2004, 2005, 2006, 2007 Apple Inc. All rights reserved.
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
@@ skipping 163 matching lines @@
 bool ImageResource::CanReuse(const FetchParameters& params) const {
   // If the image is a placeholder, but this fetch doesn't allow a
   // placeholder, then do not reuse this resource.
   if (params.GetPlaceholderImageRequestType() !=
           FetchParameters::kAllowPlaceholder &&
       placeholder_option_ != PlaceholderOption::kDoNotReloadPlaceholder)
     return false;
   return true;
 }
 
+bool ImageResource::CanUseCacheValidator() const {
+  // Disable revalidation while ImageResourceContent is still waiting for
+  // SVG load completion.
+  // TODO(hiroshige): Clean up revalidation-related dependencies.
+  if (!GetContent()->IsLoaded())

[hiroshige, 2017/05/04 22:50:50]

This is not clean, but ImageResourceContent has already special logics for
revalidation (e.g. IsCacheValidator() call in AddObserver()).

However, I expect allowing revalidation during waiting for SVG load complicates
the state transition much more.
Consider the following scenario:
(1) DidFinishLoading() for an SVG image is called, and we start waiting SVG load
completion. GetContentState() is kPending.
(2) Revalidation starts.
(3) SVG load completes.
    At this time, I think we shouldn't notify observers nor change the state to
kCached, because we are in the middle of revalidation.
(4) Revalidation response is received and its 304.
    The original SVG image continues to be used, and thus we have to notify its
load completion. Therefore, we have to remember the notification at Step (3) and
then process it here in Step (4).

+    return false;
+
+  return Resource::CanUseCacheValidator();
+}
+
 ImageResource* ImageResource::Create(const ResourceRequest& request) {
   return new ImageResource(request, ResourceLoaderOptions(),
                            ImageResourceContent::Create(), false);
 }
 
 ImageResource::ImageResource(const ResourceRequest& resource_request,
                              const ResourceLoaderOptions& options,
                              ImageResourceContent* content,
                              bool is_placeholder)
     : Resource(resource_request, kImage, options),
@@ skipping 407 matching lines @@
     //    reloading in Step 3 due to notifyObservers()'s
     //    schedulingReloadOrShouldReloadBrokenPlaceholder() check.
     // 3. reloadIfLoFiOrPlaceholderImage() is called via ResourceFetcher
     //    (a) via didFinishLoading() called in decodeError(), or
     //    (b) after returning ImageResource::updateImage().
     DecodeError(all_data_received);
   }
 }
 
 }  // namespace blink