Run cros_x86 trybots on changes to ^(base|build|chromeos).*\.gypi?$.

Since the full chromeos builders are sensitive to high level gypi
changes, make sure to do full tryjobs on them in addition to the faster
linux_chromeos bots when gyp files change.

BUG=none
R=maruel@chromium.org, phajdan.jr@chromium.org

Review URL: https://codereview.chromium.org/24366005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226033 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226033