Bug 1040561 - Part 2. Don't wait Nuwa preallocated process when allocating new browser process. r=khuey

This makes the browser process allocation behavior align to the app
process allocation.
Bug 1040561 - Part 3. Return nullptr when CreateContentBridgeParent fails. r=khuey
Bug 1040561 - Part 4. Initialize mOpener when transform preallocated process. r=khuey
Bug 1040561 - Part 5. Initialize mManager in TabChild::Create. r=khuey