Use a direct include of strings headers in base/.

base/metrics/sparse_histogram_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 "base/memory/scoped_ptr.h"
 #include "base/metrics/histogram_base.h"
 #include "base/metrics/histogram_samples.h"
 #include "base/metrics/sample_map.h"
 #include "base/metrics/sparse_histogram.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/pickle.h"
-#include "base/stringprintf.h"
+#include "base/strings/stringprintf.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
 
 class SparseHistogramTest : public testing::Test {
  protected:
   virtual void SetUp() {
     // Each test will have a clean state (no Histogram / BucketRanges
     // registered).
     InitializeStatisticsRecorder();
@@ skipping 110 matching lines @@
 
   int flag;
   EXPECT_TRUE(iter.ReadInt(&flag));
   EXPECT_EQ(HistogramBase::kIPCSerializationSourceFlag, flag);
 
   // No more data in the pickle.
   EXPECT_FALSE(iter.SkipBytes(1));
 }
 
 }  // namespace base