Fix the embedded build

Adopt to toolchain changes and fix the build with the
current snapshot.
This patch adds some missing overrides and build system
configurations.

Change-Id: I488929500347bdb5a077ac14e9553cedfcaa605d
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>
Clean up qtwebengine.gypi

Fix the indentation and remove some obsolete settings.

Change-Id: I59d3c00f481b2ae124e1b3a6434ff5c68acde53d
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>
Move the implementation of BrowserContextQt to its own cpp file

Change-Id: Ie44a8733e3f9123c3d086f8df9ddcf2833bd235b
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>