Added automated performance test to TileBenchmark

bug:5062896

Depends on external/webkit change:
https://android-git.corp.google.com/g/#change,125566

Loads pages from SD card, and scrolls through them reporting results. Added
contentInvalidateAll hidden WebView method, and made pageSwapCallback
extensible.

Change-Id: I9f7377aad6fd7c101177dde552a72357c8b4e400