Use a direct include of strings headers in ppapi/, printing/.

ppapi/proxy/ppb_var_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <string>
 #include <vector>
 
-#include "base/string_number_conversions.h"
+#include "base/strings/string_number_conversions.h"
 #include "base/threading/platform_thread.h"
 #include "ppapi/c/pp_var.h"
 #include "ppapi/c/ppb_var.h"
 #include "ppapi/proxy/ppapi_proxy_test.h"
 #include "ppapi/shared_impl/ppb_var_shared.h"
 
 namespace {
 std::string VarToString(const PP_Var& var, const PPB_Var* ppb_var) {
   uint32_t len = 0;
   const char* utf8 = ppb_var->VarToUtf8(var, &len);
@@ skipping 213 matching lines @@
   for (size_t i = 0; i < kNumStrings; ++i) {
     uint32_t len = 10;
     const char* utf8 = ppb_var_->VarToUtf8(vars_[i], &len);
     EXPECT_EQ(NULL, utf8);
     EXPECT_EQ(0u, len);
   }
 }
 
 }  // namespace proxy
 }  // namespace ppapi