Revert "Browser: disable incognito mode"

This reverts commit 5623a091605bf1d88687dc589a61ee6b54c554fe.

 This is the 2nd commit message:

Revert "Browser: fix pie crash"

This reverts commit 06929f1b1103f5a5651a8fc71e6b6e6b10bde71d.

Change-Id: I23f2e34ee125785bba8981f0611ba4986a9beaab
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
Always show the action bar overflow

As with native action bars.

Change-Id: I460ee02b370d7f220a8702d2e7644a7c775e3b21