Remove the require_gesture member from BeforeInstallPromptEvent.

Chrome's implementation of this web platform feature always requires a
user gesture to trigger now. Remove the option and plumbing that passes
the require_gesture boolean (which is now always set to true).

TBR=mkwst@chromium.org
BUG=869780

Change-Id: Iebdd435d8df3baf0996c01eda660b6074affde9b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1735089
Commit-Queue: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Alan Cutter <alancutter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683906}
7 files changed