Fix browser hang due to plugin deadlock...

Fix browser hang due to plugin deadlock

This involves two plugin instances with second instance making 
sync calls to the renderer while the first one is still servicing
an incoming sync request.

Our logic to unblock the renderer during the sync call fails 
since the 'in_dispatch_' counter is maintained per plugin channel 
(each plugin instance uses its own separate channel). Making 
'in_dispatch_' counter static member of PluginChannelBase fixes this 
deadlock.

Added a new NPAPI UI test for this scenario.

BUG=12624
TEST=MultipleInstancesSyncCalls


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=17492

[ananta, 2009-06-03 17:08:36]

LGTM

http://codereview.chromium.org/119052/diff/32/34
File webkit/glue/plugins/test/plugin_windowless_test.cc (right):

http://codereview.chromium.org/119052/diff/32/34#newcode67
Line 67: "parent.document.getElementById('frame').outerHTML = ''", NULL);
You may want to move the parameters to the next line.

[jam, 2009-06-04 06:35:27]

The real problem is that there is more than one channel between a plugin and
renderer process.  This is a regression from some earlier changes that I made.