Integrate the Windows 8 code into the Chromium tree (take 3).

Integrate the Windows 8 code into the Chromium tree (take 3).

This time, also:
fix invalid path in metro_driver.gyp.
set executable bit on check_sdk_patch.py and post_build.bat.
add back a switch that was removed recently

This reverts "Revert 155429 - Integrate the Windows 8 code into the Chromium tree."

Original CL: https://chromiumcodereview.appspot.com/10875008

BUG=127799
TEST=A Chromium build can run as the immersive browser on Windows 8.
TBR=ben

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=155474