Refactor PushClientChannel
Move code responsible for working with invalidations library out of
PushClientChannel into SyncNetworkChannel. PushClientChannel only has
code related to PushClient.
Create PushClient independent SyncNetworkChannel::Observer interface and
make SyncInvalidationListener observe it instead of PushClientObserver.
Move ownership of PushClientChannel from SyncSystemResources to
SyncInvalidationListener.
Tests for PushClientChannel are still in push_client_channel_unittest.cc.
I'll split those in subsequent patch.
BUG=325020
Review URL: https://codereview.chromium.org/
103223004
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239176 0039d316-1c4b-4281-b951-d872f2087c98