Improve process crash handling in RenderViewHost & mock RenderProcessHost.

Currently the mock RenderProcessHost always lies about having a connection
to the renderer process. This CL aims to make it more realistic by keeping
track of process initialization and crashing.

Additionally, RenderViewHost can directly monitor the RenderProcessHost
for crashes instead of relying on the RenderFrameHost to notify it.
The CL includes the decoupling of the two.

BUG=357747

Review URL: https://codereview.chromium.org/1159183002

Cr-Commit-Position: refs/heads/master@{#332462}
14 files changed