gl_context_linux.cc(294) Pbuffer support not available. failed to create pixmap

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What steps will reproduce the problem?
1. Install latest nightly build on Linux 64bit system (2.6.31 Karmic Koala)
2. Run chrome with parameter "--enable-webgl"
3. Visit any webgl demo page. (http://wakaba.c3.cx/w/escher_droste.html)

What is the expected output? What do you see instead?
Expected to see rendered scene. Instead, I see error messages stating the 
plugin is not installed.

What version of the product are you using? On what operating system?
Chromium 6.0.426.0 (48995)

What hardware are you using:  graphics card type?  motherboard type?
VGA compatible controller: ATI Technologies Inc RV530 [Radeon X1600]

Please provide any additional information below.

[15272:15272:97033727374:ERROR:app/gfx/gl/gl_context_linux.cc(294)] Pbuffer 
support not available.
failed to create pixmap
The program 'exe' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadDrawable (invalid Pixmap or Window parameter)'.
  (Details: serial 138 error_code 9 request_code 135 minor_code 7)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() 
function.)

Original issue reported on code.google.com by [e-mail] on 5 Jun 2010 at 3:20