Drop all uses of //base except ObserverList from view mgr client lib

mojo/services/view_manager/public/cpp/lib/view_observer.cc

Index: mojo/services/view_manager/public/cpp/lib/view_observer.cc
diff --git a/mojo/services/view_manager/public/cpp/lib/view_observer.cc b/mojo/services/view_manager/public/cpp/lib/view_observer.cc
index 456147cceb92d2f77edc2241fe65bdf448af6916..7e6acc0c3f36c44f60294a0c65c350d2acd0561b 100644
--- a/mojo/services/view_manager/public/cpp/lib/view_observer.cc
+++ b/mojo/services/view_manager/public/cpp/lib/view_observer.cc
@@ -4,17 +4,16 @@
 
 #include "view_manager/public/cpp/view_observer.h"
 
-#include "base/basictypes.h"
-
 namespace mojo {
 
 ////////////////////////////////////////////////////////////////////////////////
 // ViewObserver, public:
 
 ViewObserver::TreeChangeParams::TreeChangeParams()
-    : target(NULL),
-      old_parent(NULL),
-      new_parent(NULL),
-      receiver(NULL) {}
+    : target(nullptr),
+      old_parent(nullptr),
+      new_parent(nullptr),
+      receiver(nullptr) {
+}
 
 }  // namespace mojo