ime: Add metrics for mode change key.

We want to know:

1) Overall usage
2) What was result of pressing the key.

We also expanded ImeSwitch enum to include the key.

Bug: 953901
Change-Id: I0a59bfd836cdd9c56d68449f3417dfda7132ef18
Reviewed-by: Charlie Harrison <>
Reviewed-by: Scott Violet <>
Commit-Queue: Darren Shen <>
Cr-Commit-Position: refs/heads/master@{#661500}
4 files changed