Convert //base to use std::unique_ptr

base/files/file_util.cc

Index: base/files/file_util.cc
diff --git a/base/files/file_util.cc b/base/files/file_util.cc
index 31693704d6761e414ecc34b33809a15e03b21b1c..80fa44f9ea22648fb7b9e9a55e67a049abcb66c0 100644
--- a/base/files/file_util.cc
+++ b/base/files/file_util.cc
@@ -137,7 +137,7 @@ bool ReadFileToStringWithMaxSize(const FilePath& path,
   }
 
   const size_t kBufferSize = 1 << 16;
-  scoped_ptr<char[]> buf(new char[kBufferSize]);
+  std::unique_ptr<char[]> buf(new char[kBufferSize]);
   size_t len;
   size_t size = 0;
   bool read_status = true;