Remove id attribute from inner editor element.

This forces the UA shadow root to create a number of data structures, and for
this use case they are adequately replaced by a single native Oilpan member.

On my workstation, this shows up as using about 1.3% of the CPU time in the
Speedometer jQuery TodoMVC app.

Change-Id: I5de4fcbd86920f447399c07f57d5b0f382a3216b
Reviewed-on: https://chromium-review.googlesource.com/734233
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Reviewed-by: Keishi Hattori <keishi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512185}
80 files changed