Allow 'chrome-extension:' URLs to bypass content settings (1/2)

Merge "Allow 'chrome-extension:' URLs to bypass content settings (1/2)" to M46.

> We changed the behavior of 'Document::firstPartyForCookies' to return an
> empty URL in the case where any URL in the ancestor chain doesn't match
> the current document's URL. Previously, we'd simply return the top-level
> document's URL.
>
> This means that the content-settings bypass check in
> 'ContentSettingsObserver::IsWhitelistedForContentSettings' sees an empty
> URL as opposed to a 'chrome-extension://' URL for cases in which an
> extension loads a resource, so content settings are applied as per usual.
> This breaks things fairly badly for folks who have turned on third-party
> cookie blocking.
>
> In these patches, we introduce a new scheme registry for those schemes
> which ought to override Blink's concept of "first-party" when they're
> loaded into the top-level browsing context.
>
> Patch 1 (Blink): https://codereview.chromium.org/1305253012
> Patch 2 (Chromium): [This patch]
>
> BUG=527963
> R=jochen@chromium.org
>
> Review URL: https://codereview.chromium.org/1332563006

Cr-Commit-Position: refs/heads/master@{#348194}
(cherry picked from commit cfed7a300606c5eedb858433b37db5ffadf3b2cc)

Note: Moved the call of this method from Dispatcher::WebKitInitialized()
to Dispatcher::Dispatcher(), which is where the similar methods were at
this point in history.

TBR=amineer@chromium.org

Committed: https://chromium.googlesource.com/chromium/src/+/c82b0ab685fef68670557b095dfc960f2086417f

[Mike West, 2015-09-18 09:03:07]

Committed patchset #1 (id:1) manually as
c82b0ab685fef68670557b095dfc960f2086417f (presubmit successful).