Return HTTP headers even if there is no HTTP response body.

Also add a test to demonstrate that we've bug 7787.
http://code.google.com/p/android/issues/detail?id=7787

Change-Id: I4e320835516c05ec9e305661b5bbb1e59b278183
tree: 4b825dc642cb6eb9a060e54bf8d69288fbee4904

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