cc: Update draw if external draw constraints change

BUG=388056

Review URL: https://codereview.chromium.org/351673008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@279497 0039d316-1c4b-4281-b951-d872f2087c98

cc/trees/layer_tree_host_impl.cc

@@ -1309,6 +1309,10 @@ void LayerTreeHostImpl::SetExternalDrawConstraints(
     const gfx::Rect& viewport,
     const gfx::Rect& clip,
     bool valid_for_tile_management) {
+  if (external_transform_ != transform || external_viewport_ != viewport) {
+    active_tree_->set_needs_update_draw_properties();
+  }
+
   external_transform_ = transform;
   external_viewport_ = viewport;
   external_clip_ = clip;

cc/trees/layer_tree_host_impl_unittest.cc

@@ -6578,5 +6578,31 @@ TEST_F(LayerTreeHostImplWithImplicitLimitsTest, ImplicitMemoryLimits) {
             150u * 1024u * 1024u);
 }
 
+TEST_F(LayerTreeHostImplTest, ExternalTransformReflectedInNextDraw) {
+  const gfx::Size layer_size(100, 100);
+  gfx::Transform external_transform;
+  const gfx::Rect external_viewport(layer_size);
+  const gfx::Rect external_clip(layer_size);
+  const bool valid_for_tile_management = true;
+  LayerImpl* layer = SetupScrollAndContentsLayers(layer_size);
+
+  host_impl_->SetExternalDrawConstraints(external_transform,
+                                         external_viewport,
+                                         external_clip,
+                                         valid_for_tile_management);
+  DrawFrame();
+  EXPECT_TRANSFORMATION_MATRIX_EQ(
+      external_transform, layer->draw_properties().target_space_transform);
+
+  external_transform.Translate(20, 20);
+  host_impl_->SetExternalDrawConstraints(external_transform,
+                                         external_viewport,
+                                         external_clip,
+                                         valid_for_tile_management);
+  DrawFrame();
+  EXPECT_TRANSFORMATION_MATRIX_EQ(
+      external_transform, layer->draw_properties().target_space_transform);
+}
+
 }  // namespace
 }  // namespace cc