Revert 219709 "Remove the Extensions URLRequestContext."

Revert 219709 "Remove the Extensions URLRequestContext."

Reverted due to crashes under memory tools.
BUG=280138
> Remove the Extensions URLRequestContext.
> 
> Though chrome-extension: scheme URLs support cookies, they do not share
> a namespace with http: and https:. In particular, chrome-extension://a and
> http://a should not have the same set of cookies.
> 
> To enforce this, previously the code created a completely separate
> URLRequestContext for servicing chrome-extension: schemes. However,
> the code really only used this object as a method for conveying the
> correct cookie jar from Profile creation to a few spots where cookies
> were accessed; the rest of the URLRequestContext functionality was unused.
> 
> This CL removes the Extensions URLRequestContext code and replaces it
> with APIs that directly expose the needed net::CookieStore.
> 
> Lastly, CookieMonster::EnableFileScheme() is removed and 
> CookieMonster::Delegate is renamed CookieMonsterDelegate.
> 
> EnableFileScheme is an inherently racy API because 
> CookieMonsters are creatable on all threads and this 
> function sets an unprotected global flag. CookieMonsterDelegate
> is preferable to the nested interface because it can now be
> forward declared.
> 
> TBRing darin and sky to cover the rest of the mechanical unittest changes.
> 
> TBR=darin,sky
> BUG=158386, 159193, 57884
> 
> Review URL: https://chromiumcodereview.appspot.com/12546016

TBR=ajwong@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=219787

[earthdok, 2013-08-27 14:39:13]

Committed patchset #1 manually as r219787 (presubmit successful).