Move stringpiece.h and stringprintf.h to base/.

Change-Id: I7f71b4a12f99c5f81771146c66629ae5a947b229
diff --git a/src/jni_internal.cc b/src/jni_internal.cc
index fc7bdd4..6e40cf4 100644
--- a/src/jni_internal.cc
+++ b/src/jni_internal.cc
@@ -25,6 +25,7 @@
 #include "base/logging.h"
 #include "base/mutex.h"
 #include "base/stl_util.h"
+#include "base/stringpiece.h"
 #include "class_linker.h"
 #include "class_loader.h"
 #include "invoke_arg_array_builder.h"
@@ -35,7 +36,6 @@
 #include "safe_map.h"
 #include "scoped_thread_state_change.h"
 #include "ScopedLocalRef.h"
-#include "stringpiece.h"
 #include "thread.h"
 #include "UniquePtr.h"
 #include "well_known_classes.h"