Rework tree APIs to reflect Google style and more const-correctness....

views/layout/fill_layout.cc

Index: views/layout/fill_layout.cc
===================================================================
--- views/layout/fill_layout.cc	(revision 74117)
+++ views/layout/fill_layout.cc	(working copy)
@@ -15,7 +15,7 @@
 }
 
 void FillLayout::Layout(View* host) {
-  if (host->GetChildViewCount() == 0)
+  if (!host->has_children())
     return;
 
   View* frame_view = host->GetChildViewAt(0);
@@ -23,7 +23,7 @@
 }
 
 gfx::Size FillLayout::GetPreferredSize(View* host) {
-  DCHECK(host->GetChildViewCount() == 1);
+  DCHECK(host->child_count() == 1);
   return host->GetChildViewAt(0)->GetPreferredSize();
 }