Clear SingleProcess and InProcessGPU logic.

1. SingleProcess and InProcessGPU mode are not supported in multiple-dll mode
currently. Add CHECK() in RunNamedProcessTypeMain().

2. GPU Process.
1) Currently, if InProcessGPU mode is enabled and g_gpu_main_thread_factory is
not set, launch GPU Process slightly. However, other InProcessGPU code does not check if
g_gpu_main_thread_factory is not set. It is a potential bug.

2) GpuMain() can not be called when SingleProcess or InProcessGPU mode. Remove
SingleProcess and InProcessGPU switch check code.

3. Currently, if SingleProcess mode is enabled and g_renderer_main_thread_factory
is not set, launch Render Process slightly. It is a potential bug.

4. Currently, if SingleProcess mode is enabled and g_utility_main_thread_factory
is not set, launch Utility Process slightly. It is a potential bug.

Review URL: https://codereview.chromium.org/65193003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237011 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237011