[bfcache] Add a chrome://flag for back-forward cache

Make it easier (or possible) to test bfcache on Android devices by
exposing a flag via chrome://flags page.

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Change-Id: If233505268bec27d2aa616ab1d5679e2a1ac3e84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1807317
Reviewed-by: Arthur Sonzogni <[email protected]>
Commit-Queue: Alexander Timin <[email protected]>
Auto-Submit: Alexander Timin <[email protected]>
Cr-Commit-Position: refs/heads/master@{#697170}
5 files changed