Revert "Pepper: Fix channel init in ProxyChannel."

This reverts:
https://src.chromium.org/viewvc/chrome?view=rev&revision=253408
because it introduces a data race. See:
https://code.google.com/p/chromium/issues/detail?id=244383

This CL might still be a good change, but there will need to
be changes to IPC::ChannelProxy first.

BUG=343768
TBR=teravest

Review URL: https://codereview.chromium.org/179873019

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253978 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253978