WebLayer: hook up spellcheck on Android.

WebLayer uses the same implementation as WebView. What it lacks compared
to Clank is just metrics. That is, the parts of
//chrome/browser/spellchecker that Clank actually uses are purely
metrics as the spelling service is not enabled for Clank.

Implementing spellcheck for desktop would require refactoring a lot of
//chrome/browser/spellchecker.

Bug: 1025621
Change-Id: I186f78c08d97267cb8d55e55adff952018293840
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1929494
Commit-Queue: Evan Stade <[email protected]>
Reviewed-by: Scott Violet <[email protected]>
Cr-Commit-Position: refs/heads/master@{#721708}
8 files changed