Add didChangePriority() to ResourceHandle
https://bugs.webkit.org/show_bug.cgi?id=107995

Reviewed by Darin Fisher.

Source/Platform:

* chromium/public/WebURLLoader.h:
(WebKit):
(WebURLLoader):
(WebKit::WebURLLoader::didChangePriority): Added.

Source/WebCore:

For PLT, it's important that preloads remain a lower priority than parser requested resources.
This can lead to a 5% improvement.

The plan is to use this plumbing to expose the desired behavior. This patch simply allows a
resource's priority to change and have it propagate to the network layer. An upcoming patch will
lower the priority of preloads and then increase the priority when the parser officially requests
it.

No new tests. No visible change, because priority doesn't change yet.

* loader/cache/CachedResource.cpp:
(WebCore):
(WebCore::CachedResource::setLoadPriority):
* loader/cache/CachedResourceLoader.cpp:
(WebCore::CachedResourceLoader::requestResource): Allow loads to modify priority.
* loader/cache/CachedResourceRequest.h:
(WebCore::CachedResourceRequest::setPriority): Notify when priority changes.
* platform/network/ResourceHandle.cpp:
(WebCore::ResourceHandle::didChangePriority): Added.
(WebCore):
* platform/network/ResourceHandle.h:
(ResourceHandle):
* platform/network/chromium/ResourceHandle.cpp:
(WebCore::ResourceHandleInternal::didChangePriority):
(WebCore):
(WebCore::ResourceHandle::didChangePriority):
* platform/network/chromium/ResourceHandleInternal.h:
(ResourceHandleInternal):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@141684 268f45cc-cd09-0410-ab3c-d52691b4dbfc