Make the directx sdk and the regular sdk path a gyp variable
For the directx it probes in src\third_party\directxsdk if you have the dxsdk there and
for the regular sdk it probems in src\third_party\platformsdk_win8
If it does not find them it takes an educated guess.
The gyp variables windows_sdk_path and directx_sdk_path can be overriden from the environment if
the defaults are wrong.
BUG=none
TEST=chrome builds
Review URL: https://chromiumcodereview.appspot.com/
10690072
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@145619 0039d316-1c4b-4281-b951-d872f2087c98