gyp_chromium: Escape " for gn files.

BUG=326024
TBR=brettw@chromium.org

Review URL: https://codereview.chromium.org/106143002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238883 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238883