Add measurement for dex size.

The memory issue is due to the use of regex. Remove that and
add a simple util method to check classes dex.

Bug: 183407097
Test: run via forrest and verify the result https://fusion2.corp.google.com/invocations/99ac3b54-9dea-47aa-9f1a-f33e4a08a048/artifacts
Change-Id: I7ce5278b7fd6baa325e477ebf428b21db544cab6