enabling drag and drop

I've run into a snag enabling drag-and-drop.  The code that's failing is:

     nsCOMPtr<nsICommandManager> commandManager = 
do_GetInterface(m_web_browser);

where m_web_browser is declared like this

     nsCOMPtr<nsIWebBrowser>             m_web_browser;

and initialized as WebBrowserChrome::CreateBrowser in 
src/embedding/tests/winEmbed/WebBrowserChrome.cpp does.

The above do_GetInterface functions returns NULL.  I have logging turned 
on in gecko (all:5) and I see this in the log:

0[1584ab8]: WARNING: NS_ENSURE_TRUE(browserChrome) failed: file 
c:/utils/cygwin/home/dbyron/src/tuneup/trunk/mozilla/src/docshell/base/nsDocShell.cpp, 
line 10284
0[1584ab8]: nsComponentManager: 
CreateInstanceByContractID(@mozilla.org/embedcomp/command-manager;1) 
succeeded
0[1584ab8]: WARNING: NS_ENSURE_TRUE(browserChrome) failed: file 
c:/utils/cygwin/home/dbyron/src/tuneup/trunk/mozilla/src/docshell/base/nsDocShell.cpp, 
line 10284
0[1584ab8]: WARNING: NS_ENSURE_TRUE(aWindow) failed: file 
c:/utils/cygwin/home/dbyron/src/tuneup/trunk/mozilla/src/embedding/components/commandhandler/src/nsCommandManager.cpp, 
line 116
0[1584ab8]: WARNING: NS_ENSURE_SUCCESS(EnsureCommandHandler(), 
((nsresult) 0x80004005L)) failed with result 0x80004005: file 
c:/utils/cygwin/home/dbyron/src/tuneup/trunk/mozilla/src/docshell/base/nsDocShell.cpp, 
line 848

though I see the warning about browserChrome from line 10284 elsewhere 
in the log whether I try to get to nsICommandManager or not.

I would have thought the call to m_web_browser->SetContainerWindow would 
have gotten my nsIWebBrowserChrome implementation everywhere it needed 
to be, but I guess not.

Can anyone point me in the right direction for getting the warnings to 
go way, and more importantly, to getting an nsICommandManager so I can 
control drag-and-drop behavior?

Thanks much.

-DB