[Android] Update path to testing AndroidManifest.xml for GN.

In https://codereview.chromium.org/1071573003
the testing/android/ directory was moved into
testing/android/native_test/ which broke the
Opus test_opus_padding target. It's built as
part of the 'all' target, which is why it hasn't
been noticed (Android GN bots build chrome_shell_apk).

Review URL: https://codereview.chromium.org/1079963002

Cr-Commit-Position: refs/heads/master@{#324836}
1 file changed