Bug 781731 - Fix Azure Cairo GTK perf by removing xlib to buffered image conversion. r=mattwoodrow

gfx/thebes/gfxPlatform.cpp

@@ -535,8 +535,23 @@ gfxPlatform::GetSourceSurfaceForSurface(DrawTarget *aTarget, gfxASurface *aSurfa
       dt->Flush();
     }
     srcBuffer = aTarget->CreateSourceSurfaceFromNativeSurface(surf);
-  }
+  } else
 #endif
+  if (aSurface->CairoSurface() && aTarget->GetType() == BACKEND_CAIRO) {
+    // If this is an xlib cairo surface we don't want to fetch it into memory
+    // because this is a major slow down.
+    NativeSurface surf;
+    surf.mFormat = format;
+    surf.mType = NATIVE_SURFACE_CAIRO_SURFACE;
+    surf.mSurface = aSurface->CairoSurface();
+    srcBuffer = aTarget->CreateSourceSurfaceFromNativeSurface(surf);
+
+    if (srcBuffer) {
+      // It's cheap enough to make a new one so we won't keep it around and
+      // keeping it creates a cycle.
+      return srcBuffer;
+    }
+  }
 
   if (!srcBuffer) {
     nsRefPtr<gfxImageSurface> imgSurface = aSurface->GetAsImageSurface();