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

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=193020

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

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@193040 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/base/pickle_unittest.cc b/base/pickle_unittest.cc
index d418fdf..d252dae 100644
--- a/base/pickle_unittest.cc
+++ b/base/pickle_unittest.cc
@@ -134,7 +134,7 @@
 
 TEST(PickleTest, ZeroLenStr) {
   Pickle pickle;
-  EXPECT_TRUE(pickle.WriteString(""));
+  EXPECT_TRUE(pickle.WriteString(std::string()));
 
   PickleIterator iter(pickle);
   std::string outstr;
@@ -144,7 +144,7 @@
 
 TEST(PickleTest, ZeroLenWStr) {
   Pickle pickle;
-  EXPECT_TRUE(pickle.WriteWString(L""));
+  EXPECT_TRUE(pickle.WriteWString(std::wstring()));
 
   PickleIterator iter(pickle);
   std::string outstr;