Revert "Headless: Support multiple TabSockets"

This reverts commit c5b3efa9a0ea0b0d2e4aa28784e6d7029b7f1289.

Reason for revert: the newly added test HeadlessNoDevToolsTabSocketTest is flaky on Mac.
https://build.chromium.org/p/chromium.mac/builders/Mac10.9%20Tests%20%28dbg%29

Original change's description:
> Headless: Support multiple TabSockets
> 
> TabSockets are intended to either be installed into the main world or
> a isolated world created by Page.createIsolatedWorld.  Previously we
> only supported a single TabSocket per WebContents but that's unfortunate
> with OOPIF.  This patch lets us support multiple TabSockets up to one
> per world per frame.
> 
> The mojoms have changed a bit with
> TabSocket::AwaitNextMessageFromEmbedder moving to 
> HeadlessRenderFrameController::SendMessageToTabSocket which simplifies
> recieveing a message from the embedder since a hanging IPC is no
> longer needed.
> 
> Bug: 546953
> Change-Id: I835ffcdf3bf9acd5be687074977346fb19f69d12
> Reviewed-on: https://chromium-review.googlesource.com/543160
> Commit-Queue: Alex Clarke <alexclarke@chromium.org>
> Reviewed-by: Jochen Eisinger <jochen@chromium.org>
> Reviewed-by: Mike West <mkwst@chromium.org>
> Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
> Reviewed-by: Eric Seckler <eseckler@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#482990}

TBR=skyostil@chromium.org,alexclarke@chromium.org,eseckler@chromium.org,jochen@chromium.org,mkwst@chromium.org

Change-Id: If1c988e89b2594d88304a673c20f15888233630b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 546953
Reviewed-on: https://chromium-review.googlesource.com/553237
Reviewed-by: Rouslan Solomakhin <rouslan@chromium.org>
Commit-Queue: Rouslan Solomakhin <rouslan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#483089}
24 files changed