NPP_SetWindow can pass the wrong window's CGContextRef to a plugin. b=500130 r=josh sr=roc

widget/src/cocoa/nsChildView.mm

@@ -810,12 +810,22 @@ void* nsChildView::GetNativeData(PRUint32 aDataType)
       if ([mView isKindOfClass:[ChildView class]])
         [(ChildView*)mView setIsPluginView:YES];
 
-      mPluginPort.cgPort.context = (CGContextRef)[[NSGraphicsContext currentContext] graphicsPort];
-
       NSWindow* window = [mView nativeWindow];
       if (window) {
+        // [NSGraphicsContext currentContext] is supposed to "return the
+        // current graphics context of the current thread."  But sometimes
+        // (when called while mView isn't focused for drawing) it returns a
+        // graphics context for the wrong window.  [window graphicsContext]
+        // (which "provides the graphics context associated with the window
+        // for the current thread") seems always to return the "right"
+        // graphics context.  See bug 500130.
+        mPluginPort.cgPort.context = (CGContextRef)
+          [[window graphicsContext] graphicsPort];
         WindowRef topLevelWindow = (WindowRef)[window windowRef];
         mPluginPort.cgPort.window = topLevelWindow;
+      } else {
+        mPluginPort.cgPort.context = nil;
+        mPluginPort.cgPort.window = nil;
       }
 
       retVal = (void*)&mPluginPort;