enable -Wstring-conversion when compiling with clang

base/debug/trace_event_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/debug/trace_event_unittest.h"
 
 #include <cstdlib>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 55 matching lines @@
                          const char* value);
   bool FindNonMatchingValue(const char* key,
                             const char* value);
   void Clear() {
     trace_parsed_.Clear();
     json_output_.json_output.clear();
   }
 
   void BeginTrace() {
     event_watch_notification_ = 0;
-    TraceLog::GetInstance()->SetEnabled("*");
+    TraceLog::GetInstance()->SetEnabled(std::string("*"));
   }
 
   void EndTraceAndFlush() {
     while (TraceLog::GetInstance()->IsEnabled())
       TraceLog::GetInstance()->SetDisabled();
     TraceLog::GetInstance()->Flush(
         base::Bind(&TraceEventTestFixture::OnTraceDataCollected,
                    base::Unretained(this)));
   }
 
@@ skipping 1386 matching lines @@
   trace_log->SetEnabled(std::string("moo"));
   EXPECT_TRUE(*trace_log->GetCategoryEnabled("baz"));
   EXPECT_TRUE(*trace_log->GetCategoryEnabled("moo"));
   EXPECT_TRUE(*trace_log->GetCategoryEnabled("foo"));
   trace_log->SetDisabled();
   trace_log->SetDisabled();
 }
 
 }  // namespace debug
 }  // namespace base