QUIC - minor cleanup while merging the following change.

QUIC - minor cleanup while merging the following change.

In Chromium's AddToCache function, we use "www.google.com" instead of
empty path as it was done in the internal CL. All other changes were
already merged by rch.

Make some changes to the QuicInMemory server to clarify the interface.
Specifically that the cache is indexed by host and path, not by method
nor scheme, nor full URL, nor request headers, etc. In preparation for
making the chrome version more similar.

Merge internal change: 89092881

R=rch@chromium.org

[Ryan Hamilton, 2015-03-27 03:02:46]

lgtm