Bug 907926 - Use the ClientArea when initializing the draw target in nsWindowGfx. r=Bas

widget/windows/nsWindowGfx.cpp

@@ -367,10 +367,12 @@ bool nsWindow::OnPaint(HDC aDC, uint32_t aNestingLevel)
 
           nsRefPtr<gfxContext> thebesContext;
           if (gfxPlatform::GetPlatform()->SupportsAzureContentForType(mozilla::gfx::BACKEND_CAIRO)) {
+            RECT paintRect;
+            ::GetClientRect(mWnd, &paintRect);
             RefPtr<mozilla::gfx::DrawTarget> dt =
               gfxPlatform::GetPlatform()->CreateDrawTargetForSurface(targetSurface,
-                                                                     mozilla::gfx::IntSize(targetSurface->GetSize().width,
-                                                                                           targetSurface->GetSize().height));
+                                                                     mozilla::gfx::IntSize(paintRect.right - paintRect.left,
+                                                                                           paintRect.bottom - paintRect.top));
             thebesContext = new gfxContext(dt);
           } else {
             thebesContext = new gfxContext(targetSurface);