Fix std::string::assign invocation: pass string instead of char*.

According to the C++ standard, the three arguments overload
of std::string::assign accepts an std::basic_string:
http://en.cppreference.com/w/cpp/string/basic_string/assign

Fixing the usage, where char* instead of std::string was passed.

This popped up after libc++ became more standard compliant,
and now it throws a compiler error.

BUG=630681

Review-Url: https://codereview.chromium.org/2177653004
Cr-Commit-Position: refs/heads/master@{#407302}

net/tools/tld_cleanup/tld_cleanup_util.cc

@@ -165,7 +165,7 @@ NormalizeResult NormalizeDataToRuleMap(const std::string data,
       line_end = data.find_first_of("\r\n \t", line_start);
       if (line_end == std::string::npos)
         line_end = data.size();
-      domain.assign(data.data(), line_start, line_end - line_start);
+      domain.assign(data, line_start, line_end - line_start);
 
       Rule rule;
       rule.wildcard = false;