Fix IPC OnChannelConnected() to send correct PID on Linux/CrOS

Sandboxed renderers on Linux/CrOS are in a PID namespace, so they don't know
their own global PID. Thus the PID sent in the IPC channel Hello message
contains an unexpected value, which is used in the OnChannelConnected()
callback into chrome.

This causes problems like the Task Manager not showing any data for FPS,
JavaScript memory and image cache memory. The task manager is attempting to
use the PID/process handle from BrowserMessageFilter, which got it from
IPC::Channel::Listener::OnChannelConnected(), and it doesn't match the
global PID of each renderer.

BUG=70179
TEST=manual, open a few tabs, then open task manager, right-click to turn on JavaScript memory and image memory. Verify there are non-zero values for FPS, JavaScript memory, image cache memory

Review URL: http://codereview.chromium.org/7778031

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@99040 0039d316-1c4b-4281-b951-d872f2087c98

• content/browser/zygote_main_linux.cc[diff]
• ipc/ipc_channel.h[diff]
• ipc/ipc_channel_posix.cc[diff]
• ipc/ipc_channel_posix.h[diff]