Finalize rename of LayerImpl scroll offset methods.

This deletes stubs and renames all uses in tests for the following
methods that were renamed in https://codereview.chromium.org/800613009:

- LayerImpl::TotalScrollOffset was renamed to CurrentScrollOffset.
  TotalScrollOffset is now a LayerTreeImpl-specific concept meaning the
  sum of the inner and outer viewport current scroll offsets.
- LayerImpl::scroll_offset() was renamed to BaseScrollOffset.  This is
  the latest scroll offset pushed from the main thread.
- LayerImpl::SetScrollOffset() was renamed to
  PushScrollOffsetFromMainThread.  There are two ways to change the
  scroll offset, either pushing from the main thread or directly doing
  SetCurrentScrollOffset, corresponding to main-thread or impl-thread
  scrolling.

BUG=

Review URL: https://codereview.chromium.org/878413005

Cr-Commit-Position: refs/heads/master@{#314238}
diff --git a/cc/trees/layer_tree_host_common_unittest.cc b/cc/trees/layer_tree_host_common_unittest.cc
index 74b50113..df2b30e 100644
--- a/cc/trees/layer_tree_host_common_unittest.cc
+++ b/cc/trees/layer_tree_host_common_unittest.cc
@@ -348,7 +348,7 @@
   scroll_layer->AddChild(sublayer_scoped_ptr.Pass());
   LayerImpl* scroll_layer_raw_ptr = scroll_layer_scoped_ptr.get();
   clip_layer->AddChild(scroll_layer_scoped_ptr.Pass());
-  scroll_layer_raw_ptr->SetScrollOffset(kScrollOffset);
+  scroll_layer_raw_ptr->PushScrollOffsetFromMainThread(kScrollOffset);
 
   scoped_ptr<LayerImpl> root(LayerImpl::Create(host_impl.active_tree(), 3));
   SetLayerPropertiesForTesting(root.get(), identity_matrix, gfx::Point3F(),
@@ -7819,7 +7819,7 @@
   SetLayerPropertiesForTesting(fixed.get(), identity_transform, gfx::Point3F(),
                                gfx::PointF(3.0f, 4.0f), gfx::Size(50, 50), true,
                                false, false);
-  scroll_layer->SetScrollOffset(scroll_offset);
+  scroll_layer->PushScrollOffsetFromMainThread(scroll_offset);
   scroll_layer->SetScrollDelta(scroll_delta);
   scroll_layer->SetScrollCompensationAdjustment(main_scroll_fractional_part);