Cleanup ResourceDispatcher::PendingRequestInfo

Some preliminary cleanups for RequestPeer lifetime fix.
- Changes hash_map<> to map<scoped_ptr<>>, remove default ctor
- Replaces some linked_ptr with scoped_ptr (crbug.com/556939)

BUG=507170, 556939

Review URL: https://codereview.chromium.org/1561563002

Cr-Commit-Position: refs/heads/master@{#367782}
4 files changed