DevTools: Add a protocol method to insertText

This method emulates sending text into the page that doesn't come from
a key press. This can be used to simulate text from an emoji keyboard or
an IME.

Change-Id: I643a0ac2ba2faa4988975d87641414b6f3896301
Reviewed-on: https://chromium-review.googlesource.com/1128398
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Joel Einbinder <einbinder@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578934}
13 files changed