Make IPC channels track their peer process ID

BrokerDuplicateHandle() requires the target process ID on Windows. Rather than plumb this into every channel class independently, I'm adding it at the top.

TEST=IPCSyncChannelTest.Verified

Review URL: http://codereview.chromium.org/9968111

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@130817 0039d316-1c4b-4281-b951-d872f2087c98

• ipc/ipc_channel.h[diff]
• ipc/ipc_channel_posix.cc[diff]
• ipc/ipc_channel_posix.h[diff]
• ipc/ipc_channel_proxy.cc[diff]
• ipc/ipc_channel_proxy.h[diff]
• ipc/ipc_channel_win.cc[diff]
• ipc/ipc_channel_win.h[diff]
• ipc/ipc_sync_channel_unittest.cc[diff]