[mac] fix official build

Directly include base/string_util.h, which was removed in r53969 from the indirectly included base/command_line.h

BUG=none
TEST=Mac official builder goes green.

Review URL: http://codereview.chromium.org/3032037

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@54140 0039d316-1c4b-4281-b951-d872f2087c98

chrome/app/breakpad_mac.mm

@@ -134,8 +134,8 @@ void InitCrashReporter() {
 
   if (!is_browser) {
     // Get the guid from the command line switch.
-    std::string guid = WideToASCII(
-        command_line->GetSwitchValue(switches::kEnableCrashReporter));
+    std::string guid =
+        command_line->GetSwitchValueASCII(switches::kEnableCrashReporter);
     child_process_logging::SetClientId(guid);
    }
 }