Update tilebenchmark to work with current drawing infrastructure

bug:5062896

depends on external/webkit change: https://android-git.corp.google.com/g/#/c/154840/

- directly discard textures, instead of sending an invalidate through webkit
- better ui on smaller screens
- pass native pointer through jni calls

Change-Id: Icadbf8944edc5a2b1f8dc27bab53ac665c975462