Set main thread QoS policies after IPC initialization.
<https://webkit.org/b/134014>

Something was flipping the QoS level back to "unspecified" after
setting it in the ChildProcess initialization code. Pending a better
understanding of what really happens, move the code to a later stage,
after IPC channels are up and running. Now the priority sticks.

Reviewed by Anders Carlsson.

* NetworkProcess/NetworkProcess.cpp:
(WebKit::NetworkProcess::initializeNetworkProcess):
* Shared/ChildProcess.cpp:
(WebKit::ChildProcess::initialize):
* WebProcess/WebProcess.cpp:
(WebKit::WebProcess::initializeWebProcess):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@170100 268f45cc-cd09-0410-ab3c-d52691b4dbfc