Add media remoting unittests to media_unittests.

media/BUILD.gn

Index: media/BUILD.gn
diff --git a/media/BUILD.gn b/media/BUILD.gn
index e25c10a8c191d0aeb649c64f41025c2d686d367e..ce21b563f450a7a338ab10117350152d6a7c72da 100644
--- a/media/BUILD.gn
+++ b/media/BUILD.gn
@@ -727,6 +727,10 @@ test("media_unittests") {
       "//ui/android:ui_java",
     ]
   }
+
+  if (enable_media_remoting) {
+    deps += [ "//media/remoting:media_remoting_unittests" ]

[xhwang, 2016/10/22 00:02:33]

Does the tests work if enable_media_remoting is false? If so, we should always
enable the tests.

[xjz, 2016/10/22 00:47:43]

After discussing with miu@ offline, we decide to run these tests only when
enable_media_remoting is true, i.e., on Linux, Windows, and Mac only, because
the Media Remoting feature is only enabled on these platforms for now.

+  }
 }
 
 test("media_perftests") {