Merge r33264 from the trunk to the 249 branch....

Merge r33264 from the trunk to the 249 branch.

Add acknowledgement messages for PluginMsg_UpdateGeometry.  On the Mac, use
these acknowledgements to know when it's safe to dump old TransportDIBs in the
renderer process.  The Mac TransportDIB implementation uses
base::SharedMemory, which cannot be disposed of if an inflight UpdateGeometry
message refers to the shared memory file descriptor.

BUG=27510, 26754
TEST=1. From bug 25710:
         a. Visit http://www.dkmsoftware.com/Yubotu.htm
         b. Click "Play Now"
         c. Resize vigorously.
        Expect: no sad plugin icon.
     2. Test case from bug 26754 (affected machines only):
         a. Visit http://news.google.com/
         b. Click the [+] to the left of a YouTube link.  On affected
            machines, you'll get a sad plugin icon.
         c. Click the [+] to the left of a different YouTube link.
        Expect: no crash.
     3. Test case from bug 26754 comment 9 (affected machines only):
         a. Have lots of bookmarks (import Safari defaults)
         b. Rightclick on bookmark bar, and choose "Open All Bookmarks"
        Expect: no crash.
        This change may not actually fix the third test case.
Review URL: http://codereview.chromium.org/417005

TBR=mark@chromium.org

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=33265

[Mark Mentovai, 2009-11-30 03:35:20]

autolgtm