Add a flag to disable partial raster in renderer

cc/trees/layer_tree_host_pixeltest_tiles.cc

Index: cc/trees/layer_tree_host_pixeltest_tiles.cc
diff --git a/cc/trees/layer_tree_host_pixeltest_tiles.cc b/cc/trees/layer_tree_host_pixeltest_tiles.cc
index f013e989d3c3f9fa8adaffd068ac4aeeb38bd946..94dd0655f3646a47ea77933adbaa20f62a4d748d 100644
--- a/cc/trees/layer_tree_host_pixeltest_tiles.cc
+++ b/cc/trees/layer_tree_host_pixeltest_tiles.cc
@@ -151,6 +151,11 @@ class LayerTreeHostTilesTestPartialInvalidation
     picture_layer_->SetIsDrawable(true);
   }
 
+  void InitializeSettings(LayerTreeSettings* settings) override {
+    LayerTreeHostTilesPixelTest::InitializeSettings(settings);
+    settings->enable_partial_raster = true;
+  }
+
   void DidCommitAndDrawFrame() override {
     switch (layer_tree_host()->source_frame_number()) {
       case 1: