Add winrt to the INCLUDE directories of the toolchain bundler.

The motivation is that vcvarsall sets it, and that it might make it possible to
land https://codereview.chromium.org/405723002/ one day.

BUG=395405
TBR=jochen

Review URL: https://codereview.chromium.org/393233004

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@284349 0039d316-1c4b-4281-b951-d872f2087c98

win_toolchain/toolchain2013.py

@@ -383,6 +383,7 @@ def GenerateSetEnvCmd(target_dir, pro):
             'set PATH=%~dp0..\\..\\Common7\\IDE;%PATH%\n'
             'set INCLUDE=%~dp0..\\..\\win8sdk\\Include\\um;'
                '%~dp0..\\..\\win8sdk\\Include\\shared;'
+               '%~dp0..\\..\\win8sdk\\Include\\winrt;'
                '%~dp0..\\..\\VC\\include;'
                '%~dp0..\\..\\VC\\atlmfc\\include\n'
             'if "%1"=="/x64" goto x64\n')