[Android] Introduce state machine in stylus text selection

Stylus text selection state is handled using 2 variables
draaging_ and dragged_. Since both having similar semantics,
we can merge using a state machine.

BUG=

Review-Url: https://codereview.chromium.org/2885243003
Cr-Commit-Position: refs/heads/master@{#473046}
2 files changed