Refactoring DevTools bridge tests: moving interface adapters to SignalingReceiverProxy.

Refactoring DevTools bridge tests: moving interface adapters to SignalingReceiverProxy.

Benefits of this refactoring are:
1. Removed a redundant adapter.
2. Removed an unnecessary interface conversion (A->B->A).
3. Removed from ClientSessionTestingHost references to unrelated class LocalSessionBridge.
4. Reduced number of public classes.

BUG=383418
Committed: https://crrev.com/3508300bbf47fed5db4f0bcd8f11320c8439ba3b
Cr-Commit-Position: refs/heads/master@{#302615}

[SeRya, 2014-11-04 11:35:18]

serya@chromium.org changed reviewers:
+ mnaganov@chromium.org

[SeRya, 2014-11-04 11:35:19]

PTAL

[mnaganov (inactive), 2014-11-04 15:44:28]

lgtm

[SeRya, 2014-11-04 15:45:09]

The CQ bit was checked by serya@chromium.org

[commit-bot: I haz the power, 2014-11-04 15:47:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/700833002/1

[commit-bot: I haz the power, 2014-11-04 16:34:12]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-11-04 16:34:58]

Patchset 1 (id:??) landed as
https://crrev.com/3508300bbf47fed5db4f0bcd8f11320c8439ba3b
Cr-Commit-Position: refs/heads/master@{#302615}