Present Metal drawable with a transaction only when on the Main thread.

shell/gpu/gpu_surface_metal.mm

@@ -58,6 +58,11 @@
 
   ReleaseUnusedDrawableIfNecessary();
 
+  // When there are platform views in the scene, the drawable needs to be presented in the same
+  // transaction as the one created for platform views. When the drawable are being presented from
+  // the raster thread, there is no such transaction.
+  layer_.get().presentsWithTransaction = [[NSThread currentThread] isMainThread];
+
   auto surface = SkSurface::MakeFromCAMetalLayer(context_.get(),            // context
                                                  layer_.get(),              // layer
                                                  kTopLeft_GrSurfaceOrigin,  // origin