Remove grab-bag includes of v8.h from several files.

src/cached-powers.cc

Index: src/cached-powers.cc
diff --git a/src/cached-powers.cc b/src/cached-powers.cc
index 5bd0884eba77f1cbdc274751c524200dd2c528ea..52fff7e14560b507f895981eb6d70622f62b74a8 100644
--- a/src/cached-powers.cc
+++ b/src/cached-powers.cc
@@ -2,13 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "src/cached-powers.h"
+
 #include <limits.h>
 #include <stdarg.h>
 #include <stdint.h>
 #include <cmath>
 
 #include "src/base/logging.h"
-#include "src/cached-powers.h"
 #include "src/globals.h"
 
 namespace v8 {