This CL adds client.toDataURL which gets the contents...

plugin/idl/client.idl

Index: plugin/idl/client.idl
===================================================================
--- plugin/idl/client.idl	(revision 22687)
+++ plugin/idl/client.idl	(working copy)
@@ -475,13 +475,23 @@
   void InvalidateAllParameters();
 
   %[
-    This function is only available in the test version of the plugin.
-    \param file_name Name to save screenshot to.
-    \return True on success.
+    Gets a copy of the current backbuffer of O3D as a data: url.
+
+    NOTE: Calling it will cause a render to happen.
+
+    \return A Data URL for the backbuffer.
   %]
-  bool SaveScreen(String file_name);
+  String ToDataURL();
 
   %[
+    Gets a copy of the current backbuffer of O3D as a data: url.
+    \param mime_type The type of data url you want. Currently O3D only supports
+       image/png. See HTML5 canvas tag for info about toDataURL.
+    \return A Data URL for the backbuffer.
+  %]
+  [userglue] String ToDataURL(String mime_type);
+
+  %[
     Returns the status of initializing the renderer so we can display the
     appropriate message. We require a certain minimum set of graphics
     capabilities. If the user's computer does not have his minimum
@@ -574,6 +584,12 @@
           &modes);
       return modes;
     }
+    o3d::String userglue_method_ToDataURL(o3d::Client* self,
+                                          const o3d::String& mime_type) {
+        // We ignore the mime_type since it's only a suggestion
+        // and we only return the required image/png type.
+        return self->ToDataURL();
+    }
     void userglue_method_SetFullscreenClickRegion(
         void *plugin_data, o3d::Client *self, int x, int y, int width,
         int height, int mode_id) {