Add an API to manage local data (cookies, local storage, app cache, indexed DB and web DB)

Here's a couple of important use-cases for being able to read browser cookies:
- Transfer cookies from the Browser app to the webapp container
- Transfer cookies from Online Accounts to the webapp container

We are currently experimenting with reading the cookies straight from the SQLite database, but we find that they aren't always on sync. At the very least, we'd need to have a way to trigger the flush of the cookies to the DB.

Can we prioritize adding an API to clear disk cache first? This is really needed in devices like krillin where the disk space is extremely limited. Clearing cookies would be the second priority in my opinion.

From IRC discussion today:

 <chrisccoulson> The kind of API I'd like to see is something like clearSiteData(flags, origin, time), where flags is a bitwise OR of things like app cache, cookies, local storage etc and time specifies how far back in history to delete
 <chrisccoulson> although, specifying an origin probably wouldn't be appropriate for all types of storage
 <chrisccoulson> It would also need a way for an application to track progress - ie, clearSiteData() would return an object with a completed signal or something
 <chrisccoulson> Of course, my API idea might not make sense either - particularly if there are lots of storage types in Chromium that we don't have such control over

This bug was fixed in the package webbrowser-app - 0.23+15.04.20150408-0ubuntu1

---------------
webbrowser-app (0.23+15.04.20150408-0ubuntu1) vivid; urgency=medium

  [ CI Train Bot ]
  * New rebuild forced.
  * Resync trunk.

  [ Olivier Tilloy ]
  * Add a "Clear Cache" entry under the privacy settings. (LP: #1296364,
    #1260014)
  * Add settings page, per design specification. This adds qml-module-
    qt-labs-folderlistmodel and qml-module-qt-labs-settings as runtime
    dependencies for webbrowser-app. (LP: #1351183)
  * Autopilot tests for the settings UI. added:
    tests/autopilot/webbrowser_app/tests/test_settings.py

  [ Riccardo Padovani ]
  * Add settings page, per design specification. This adds qml-module-
    qt-labs-folderlistmodel and qml-module-qt-labs-settings as runtime
    dependencies for webbrowser-app. (LP: #1351183)
  * Add settings page, per design specification. This adds qml-module-
    qt-labs-folderlistmodel and qml-module-qt-labs-settings as runtime
    dependencies for webbrowser-app. (LP: #1351183)
 -- CI Train Bot <email address hidden> Wed, 08 Apr 2015 14:09:36 +0000

This is implemented as BrowsingDataRemover in chrome (chrome/browser/browsing_data/browsing_data_remover.h).

Another important use case is autofill profiles (see bug #1214048).

This is separate from autofill profiles, but will be necessary to clear site-specific autocomplete data.