[SPDY] Avoid leaking bytes from the session flow control send window

Add a ConsumeSource parameter to SpdyBuffer::ConsumeCallback. Use
it to detect when a DATA frame to be written is dropped before it
is written.

Put all the flow control functions together and clean them up a bit.

BUG=176592

Review URL: https://chromiumcodereview.appspot.com/14188025

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@194851 0039d316-1c4b-4281-b951-d872f2087c98
8 files changed