Android Studio: Run `gn gen` if necessary

Specifically when passing in targets manually. The `--all` flag (on by
default) already takes care of this case.

Bug: 620034
Change-Id: Ie5c679c6cf9b75e36415d2868f7fff46e9e81ad1
Reviewed-on: https://chromium-review.googlesource.com/1089121
Commit-Queue: Peter Wen <wnwen@chromium.org>
Commit-Queue: Eric Stevenson <estevenson@chromium.org>
Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#564979}
1 file changed