[Android] Generate scripts at build time to run android tests.

media/BUILD.gn

Index: media/BUILD.gn
diff --git a/media/BUILD.gn b/media/BUILD.gn
index b01ad89b1c8e1182b659d49d5d982fe95200eb1a..a4f8e1c9b356fe9a5c4030d70bcc711c53663b17 100644
--- a/media/BUILD.gn
+++ b/media/BUILD.gn
@@ -566,6 +566,8 @@ test("media_unittests") {
     "//url",
   ]
 
+  isolate_file = "media_unittests.isolate"
+
   if (is_android) {
     deps += [
       "//media/base/android",
@@ -658,6 +660,7 @@ test("media_perftests") {
   ]
   if (is_android) {
     deps += [ "//ui/gl" ]
+    isolate_file = "media_perftests.isolate"
   }
   if (media_use_ffmpeg) {
     deps += [ "//third_party/ffmpeg" ]  # Direct dependency required to inherit config.