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This flag is used by enabling an experimental IME Mojo service to
replace the existing IME framework, the project might last for a few
quarters until we are confident to get rid of old system.

Before that, we want to keep the fallback possibility for users

Change-Id: I010a8d3b21c7ff9e7a8a706bf604a1e501518717
Reviewed-on: https://chromium-review.googlesource.com/c/1345789Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Leo Zhang <googleo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612509}