[Android WebView] Add MappedHostResolver support for telemetry.

This is required for supporting new telemetry test, which use the
MappedHostResolver (via the command line switch --host-resolver-rules)
to redirect web requests to the local web page relay.

BUG=None
TEST=build/android/test_runner.py instrumentation --test_data webview:android_webview/test/data/device_files --test-apk=AndroidWebViewTest

Review URL: https://codereview.chromium.org/88243002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237578 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237578