De-duplicate common code from StringPiece, StringPiece16, and their tests.

base/string_piece_unittest.cc

Index: base/string_piece_unittest.cc
diff --git a/base/string_piece_unittest.cc b/base/string_piece_unittest.cc
index 694c43b61f5dddf1ca69406657c462f26c4028a5..d6480e1016344d1cde8854a8c53e20abdaba36f5 100644
--- a/base/string_piece_unittest.cc
+++ b/base/string_piece_unittest.cc
@@ -754,7 +754,7 @@ TEST(StringPiece16Test, CheckNULL) {
   ASSERT_EQ(s.data(), (const char16*)NULL);
   ASSERT_EQ(s.size(), 0U);
 
-  string16 str = s.as_string16();
+  string16 str = s.as_string();
   ASSERT_EQ(s.data(), (const char16*)NULL);
   ASSERT_EQ(s.size(), 0U);
 }
@@ -768,7 +768,7 @@ TEST(StringPiece16Test, CheckConversion) {
   // byte character (G clef) to test this.
   ASSERT_EQ(
       UTF16ToUTF8(
-          StringPiece16(UTF8ToUTF16("\xf0\x9d\x84\x9e")).as_string16()),
+          StringPiece16(UTF8ToUTF16("\xf0\x9d\x84\x9e")).as_string()),
       "\xf0\x9d\x84\x9e");
 }