android: Move JavaExceptionReporter to base

So that it can be used in other processes as well.
There as some comment changes, and added @MainDex. But otherwise
a straightforward move.

BUG=680775

Review-Url: https://codereview.chromium.org/2667263002
Cr-Commit-Position: refs/heads/master@{#448000}
11 files changed