Cleanup: Better constify some strings in base.

base/files/file_path.cc

Index: base/files/file_path.cc
diff --git a/base/files/file_path.cc b/base/files/file_path.cc
index ebc2d6d435bddc222a2a257780196794624847af..0db5b25548872deb2efeb28e5f5f9f74d11ec3eb 100644
--- a/base/files/file_path.cc
+++ b/base/files/file_path.cc
@@ -35,8 +35,8 @@ typedef FilePath::StringType StringType;
 
 namespace {
 
-const char* kCommonDoubleExtensionSuffixes[] = { "gz", "z", "bz2" };
-const char* kCommonDoubleExtensions[] = { "user.js" };
+const char* const kCommonDoubleExtensionSuffixes[] = { "gz", "z", "bz2" };
+const char* const kCommonDoubleExtensions[] = { "user.js" };
 
 const FilePath::CharType kStringTerminator = FILE_PATH_LITERAL('\0');