Fix double subtraction of sent_delta on sync tree activation.

cc/layers/layer_impl_unittest.cc

Index: cc/layers/layer_impl_unittest.cc
diff --git a/cc/layers/layer_impl_unittest.cc b/cc/layers/layer_impl_unittest.cc
index 99673f6146b7495e83cbf4279c58cf2308d6698f..2f778e2a744c9833b26c6f9ec6e671888095155c 100644
--- a/cc/layers/layer_impl_unittest.cc
+++ b/cc/layers/layer_impl_unittest.cc
@@ -434,6 +434,8 @@ class LayerImplScrollTest : public testing::Test {
     return host_impl_.active_tree()->root_layer()->children()[0];
   }
 
+  LayerTreeHostImpl& host_impl() { return host_impl_; }
+
   LayerTreeImpl* tree() { return host_impl_.active_tree(); }
 
   LayerTreeSettings settings() {
@@ -675,6 +677,31 @@ TEST_F(LayerImplScrollTest, ScrollUserUnscrollableLayer) {
   EXPECT_VECTOR_EQ(gfx::Vector2dF(30.5f, 5), layer()->TotalScrollOffset());
 }
 
+TEST_F(LayerImplScrollTest, PushPropertiesToMirrorsTotalScrollOffset) {
+  gfx::ScrollOffset scroll_offset(10, 5);
+  gfx::Vector2dF scroll_delta(12, 18);
+
+  host_impl().CreatePendingTree();
+
+  layer()->SetScrollOffset(scroll_offset);
+  gfx::Vector2dF unscrolled = layer()->ScrollBy(scroll_delta);
+
+  EXPECT_VECTOR_EQ(gfx::Vector2dF(0, 0), unscrolled);
+  EXPECT_VECTOR_EQ(gfx::Vector2dF(22, 23), layer()->TotalScrollOffset());
+
+  layer()->SetSentScrollDelta(scroll_delta);
+
+  scoped_ptr<LayerImpl> pending_layer =
+      LayerImpl::Create(host_impl().sync_tree(), layer()->id());
+  pending_layer->SetScrollOffset(layer()->TotalScrollOffset());
+
+  pending_layer->PushPropertiesTo(layer());
+
+  EXPECT_VECTOR_EQ(gfx::Vector2dF(22, 23), layer()->TotalScrollOffset());
+  EXPECT_VECTOR_EQ(layer()->TotalScrollOffset(),
+                   pending_layer->TotalScrollOffset());
+}
+
 TEST_F(LayerImplScrollTest, SetNewScrollbarParameters) {
   gfx::ScrollOffset scroll_offset(10, 5);
   layer()->SetScrollOffset(scroll_offset);