Retry r27137. Create renderers for ExtensionHosts one at a time to avoid blocking the UI.

Retry r27137. Create renderers for ExtensionHosts one at a time to avoid blocking the UI. 

I added a process.Close() to the fast shutdown path for renderers. The problem
was that we were trying to use an old terminated process handle.

BUG=14040
TEST=Install a bunch of extensions with toolstrips, then restart Chrome. The
UI should be responsive while the toolstrips are loading.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=27434

[Matt Perry, 2009-09-25 21:06:34]

This is the same as the last CL, but with changes to
browser_render_process_host.cc.

[Erik does not do reviews, 2009-09-25 21:10:27]

LGTM