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  * Backspace, tab, and delete are special in that they are characters,
    but non-printable.
  * This catches them and passes them through as non-printable class
    characters, so they are properly handled by blink.

Bug: internal b/174869138
Test: manual with wayland_webview_client
Change-Id: I2e33c602fbe6c85f0998717541d2f5fca0b48a5f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2625207Reviewed-by: Kevin Schoedel <kpschoedel@chromium.org>
Reviewed-by: Shawn Gallea <sagallea@google.com>
Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Commit-Queue: Ryan Daum <rdaum@chromium.org>
Cr-Commit-Position: refs/heads/master@{#842678}