Rewrite std::string("") to std::string(), Linux edition.

This patch was generated by running the empty_string clang tool
across the Chromium Linux compilation database. Implicitly or
explicitly constructing std::string() with a "" argument is
inefficient as the caller needs to emit extra instructions to
pass an argument, and the constructor needlessly copies a byte
into internal storage. Rewriting these instances to simply call
the default constructor appears to save ~14-18 kilobytes on an
optimized release build.

BUG=none

Review URL: https://codereview.chromium.org/13145003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@193020 0039d316-1c4b-4281-b951-d872f2087c98


CrOS-Libchrome-Original-Commit: e59558b78e8c6a1b0bd916a724724b638c3c91b6
diff --git a/base/file_util_unittest.cc b/base/file_util_unittest.cc
index 1f10a33..77dd7ac 100644
--- a/base/file_util_unittest.cc
+++ b/base/file_util_unittest.cc
@@ -1846,15 +1846,14 @@
 
   // create the files
   FilePath dir2file = dir2.Append(FILE_PATH_LITERAL("dir2file.txt"));
-  CreateTextFile(dir2file, L"");
+  CreateTextFile(dir2file, std::wstring());
   FilePath dir2innerfile = dir2inner.Append(FILE_PATH_LITERAL("innerfile.txt"));
-  CreateTextFile(dir2innerfile, L"");
+  CreateTextFile(dir2innerfile, std::wstring());
   FilePath file1 = temp_dir_.path().Append(FILE_PATH_LITERAL("file1.txt"));
-  CreateTextFile(file1, L"");
-  FilePath file2_rel =
-      dir2.Append(FilePath::kParentDirectory)
-          .Append(FILE_PATH_LITERAL("file2.txt"));
-  CreateTextFile(file2_rel, L"");
+  CreateTextFile(file1, std::wstring());
+  FilePath file2_rel = dir2.Append(FilePath::kParentDirectory)
+      .Append(FILE_PATH_LITERAL("file2.txt"));
+  CreateTextFile(file2_rel, std::wstring());
   FilePath file2_abs = temp_dir_.path().Append(FILE_PATH_LITERAL("file2.txt"));
 
   // Only enumerate files.