Rename contextDestroyed to contextWillBeDestroyed
Rename contextDestroyed to contextWillBeDestroyed

This CL is the devtool counterpart of the CL
https://chromium-review.googlesource.com/c/chromium/src/+/1724815.

This event is fired when the context is marked for GC,
uninitialized, and waiting for the actual destruction. Rename it
to clarify its behavior.

Bug: 970898
Change-Id: I5b9b8b601b9fec4438b47e64b6021b18b9a69b48
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1724889
Commit-Queue: Hongchan Choi <69f024f858c7ec8905f5f0e21b2e518292ce6a82@chromium.org>
Reviewed-by: Andrey Kosyakov <03b08926e49d80331ab322c2b9e0332109fbfd39@chromium.org>
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#682508}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: a85d897d5277c1cae235f5adf327c11337f14205

ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend