See bug for details of regression.

This reverts commit be0cfa14 which was:

Make Crashpad start asynchronous, and move back to chrome_elf

Crashpad initialization has been reworked to support an asynchronous
mode where StartHandler() only calls CreateThread() and does not
synchronize with that thread, making it safe to use in DllMain().

So, we can now move it back into chrome_elf to catch earlier crashes.

We block much later now in browser startup, before a renderer (i.e.
another client that would connect to the handler) will be started. This
should not be strictly necessary, but is slightly more conservative as a
first pass. This allows for error reporting, and prevents log spew from
each renderer that starts up and tries to connect to a nonexistent
handler. Also added is a UMA timer to see how long we're blocking
startup for by joining with the background thread.

TBR=mark@chromium.org, thestig@chromium.org, grt@chromium.org
BUG=700371

Review-Url: https://codereview.chromium.org/2743923003
Cr-Commit-Position: refs/heads/master@{#456221}