Revert "Incognito not supported yet in KitKat"

This reverts commit 6724f488c0b8759f359bc6f028e8ea6240f5431c.
Implement client-side incognito mode

Since WebView deprecated privateBrowsing in API 17 (and killed it
for good in API 19), we were left without incognito in the Browser
app. Follow the docs' recommendations and implement it with "manual"
control of privacy-related engine options

* Internally track incognito state for tabs
* Disable all forms of storage and cache on private webviews
* Disable all cookie activity while an incognito tab is active
* Stop trying to use the deprecated "privateBrowsing" argument
  when creating webViews, always set to false

Change-Id: I23f2e34ee125635bba8981f0711ba4986a9beaab
Show a startup page in incognito mode

Change-Id: Ib1d4be6890c81b73a46f026b6fcbb2f1e8de567d
BrowserSettings: update desktop UA string to match Chrome 30

Now that we're using a Chromium-based WebView which closely matches
Chrome 30, we should report as a newer Chrome version when masquerading
as a desktop browser.

Change-Id: I301a8cfac9a83e66a6749872943e80ff5c4740a1
Fix Memory leaks on Browser application

Working on Issue 31125 (http://code.google.com/p/android/issues
/detail?id=31125):
* Enhance mTabViews management on NavScreen class (add remove()
function when necessary).

Change-Id: I89662880107ae88ead40d5246286d4ab65ed9e75
Signed-off-by: Sebastien MICHEL <sebastien.michel@intel.com>