Allow DoLoop to be called even while no user request is pending.   Unlike the Windows implementation, our DoLoop eagerly initiates I/O between its internal buffers and the network, and we have to be ready to pump data when that completes.
Allow DoLoop to be called even while no user
request is pending.   Unlike the Windows implementation,
our DoLoop eagerly initiates I/O between its internal
buffers and the network, and we have to be ready to
pump data when that completes.

Also add debugging macros, but leave them disabled
until the next time somebody has to understand the state machine.

Fixes http://code.google.com/p/chromium/issues/detail?id=4061
Review URL: http://codereview.chromium.org/9152

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@4823 0039d316-1c4b-4281-b951-d872f2087c98

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