GitLab

With Declarative Net Request, there is no easy way for extensions to collapse
the DOM elements corresponding to the resources they blocked. This CL implements
the ability for the blocked <img> elements to be automatically collapsed in the
DOM. In subsequent CLs, similar function will be implemented for other DOM
elements.

To do this, following changes are made:
 - A new field called kCollapsedByClient is added to
   blink::ResourceRequestBlockedReason. Whenever an extension ruleset wants to
   collapse the DOM element corresponding to a network request, the
   extended_error_code is set to kCollapsedByClient, which is then used as a
   signal by the renderer to perform the collapsing.
 - Changes to blink::ResourceRequestBlockedReason also necessiate changes to the
   Devtools protocol. As a good side-effect, resources collapsed by extensions
   would be marked as "collapsed-by-client" by Devtools.
 - Changes are made to allow content embedders to set a
   blink::ResourceRequestBlockedReason for a request.

BUG=848842

Cq-Include-Trybots: luci.chromium.try:linux_mojo
Change-Id: I0bfd1a60bee79ef651741b7655fade6be4a7d419
Reviewed-on: https://chromium-review.googlesource.com/1088189
Commit-Queue: Matt Menke <mmenke@chromium.org>
Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Reviewed-by: Nate Chapin <japhet@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568332}