Fix GN Check with libcast_media_1.0_avsync

The current code includes chromecast/base, but doesn't have a GN
dependency on it.

I didn't catch this earlier because I missed turning on ENABLE_GN_CHECK
while testing locally. I wonder if that should be on by default..?

BUG=internal 73746352
TEST=Build libcast_media_1.0_avsync with ENABLE_GN_CHECK

Change-Id: I89b0103156c50f83056a5b3be5526396e0f26cd4
Reviewed-on: https://chromium-review.googlesource.com/956228
Commit-Queue: Mina Almasry <almasrymina@chromium.org>
Commit-Queue: Kenneth MacKay <kmackay@chromium.org>
Reviewed-by: Sergey Volk <servolk@chromium.org>
Reviewed-by: Kenneth MacKay <kmackay@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541865}

chromecast/media/cma/backend/video/BUILD.gn

@@ -13,6 +13,7 @@ cast_shared_library("libcast_media_1.0_avsync") {
   ]
 
   deps = [
+    "//chromecast/base:base",
     "//chromecast/media/cma/backend:for_mixer_audio",
     "//chromecast/media/cma/backend/alsa:cma_backend_support",
     "//chromecast/public",