Enable media in default GN build -- Part Deux!

Previous submission was missing enough of the android portion to prevent
passing of compilation.  This patch combines ajwong@'s previous work with
enough fixes to the Android build to get it working.

BUG=none
TEST=passes GN, compiles.
R=brettw@chromium.org

Review URL: https://codereview.chromium.org/390893003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@283477 0039d316-1c4b-4281-b951-d872f2087c98

BUILD.gn

@@ -38,6 +38,7 @@ group("root") {
     "//gpu",
     "//google_apis",
     "//ipc",
+    "//media",
     "//mojo",
     "//mojo/common",
     "//mojo/environment:chromium",

DEPS

@@ -220,7 +220,7 @@ deps = {
 
   "src/third_party/ffmpeg":
     Var("chromium_git") +
-    "/chromium/third_party/ffmpeg.git@f620cda6d1661f1b2f3214d17b9a254f5c89225f",
+    "/chromium/third_party/ffmpeg.git@4b7b36f956209fad838ad87d0129130713fbb00c",
 
   "src/third_party/libjingle/source/talk":
     (Var("googlecode_url") % "webrtc") + "/trunk/talk@" +