Improve doc of ViewObserver and clarify arguments

ui/views/view_unittest.cc

Index: ui/views/view_unittest.cc
diff --git a/ui/views/view_unittest.cc b/ui/views/view_unittest.cc
index 96cd62abd5e1563e7cbbeb889f24e5990be90452..06f33cb72a38ebccc0b0e7279b969529be174bc6 100644
--- a/ui/views/view_unittest.cc
+++ b/ui/views/view_unittest.cc
@@ -4878,11 +4878,11 @@ class ViewObserverTest : public ViewTest, public ViewObserver {
   ~ViewObserverTest() override {}
 
   // ViewObserver:
-  void OnChildViewAdded(View* child) override {
+  void OnChildViewAdded(View* parent, View* child) override {

[Bret, 2017/03/14 18:58:36]

add a couple lines to the existing unit tests that verify the parent argument is
actually the parent, for this and OnChildViewReordered below

[sky, 2017/03/14 20:19:28]

Done.

     child_view_added_times_++;
     child_view_added_ = child;
   }
-  void OnChildViewRemoved(View* child, View* parent) override {
+  void OnChildViewRemoved(View* parent, View* child) override {
     child_view_removed_times_++;
     child_view_removed_ = child;
     child_view_removed_parent_ = parent;
@@ -4898,7 +4898,9 @@ class ViewObserverTest : public ViewTest, public ViewObserver {
 
   void OnViewBoundsChanged(View* view) override { view_bounds_changed_ = view; }
 
-  void OnChildViewReordered(View* view) override { view_reordered_ = view; }
+  void OnChildViewReordered(View* parent, View* view) override {
+    view_reordered_ = view;
+  }
 
   void reset() {
     child_view_added_times_ = 0;