EXO: Conditionally bind ChromeOS APIs

APIs that have Ash dependencies can only run on ChromeOS so bind them
only when building for ChromeOS. This allows EXO to build on Chromecast.

Bug: 896710
Test: None
Change-Id: I60acf956b5a0f682f89c97b5818bb54cefcc7113
Reviewed-on: https://chromium-review.googlesource.com/c/1328702
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Commit-Queue: Daniel Nicoara <dnicoara@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611791}
1 file changed