Do not pass NULL to GetAsString().

chrome/browser/ui/ash/launcher/chrome_launcher_controller_per_browser.cc

Index: chrome/browser/ui/ash/launcher/chrome_launcher_controller_per_browser.cc
diff --git a/chrome/browser/ui/ash/launcher/chrome_launcher_controller_per_browser.cc b/chrome/browser/ui/ash/launcher/chrome_launcher_controller_per_browser.cc
index 01a4a713fbe7f2a70ae3d940f01457fa43907016..0be1d9a67f3b4991787b5ee29687e2ed7be6d0d2 100644
--- a/chrome/browser/ui/ash/launcher/chrome_launcher_controller_per_browser.cc
+++ b/chrome/browser/ui/ash/launcher/chrome_launcher_controller_per_browser.cc
@@ -194,11 +194,12 @@ std::string GetPrefForRootWindow(PrefService* pref_service,
 
     // If the pref for the specified display is not found, scan the whole prefs
     // and check if the prefs for other display is already specified.
+    std::string unused_value;
     for (base::DictionaryValue::Iterator iter(*shelf_prefs);
          !iter.IsAtEnd(); iter.Advance()) {
       const base::DictionaryValue* display_pref = NULL;
       if (iter.value().GetAsDictionary(&display_pref) &&
-          display_pref->GetString(path, static_cast<std::string*>(NULL))) {
+          display_pref->GetString(path, &unused_value)) {
         has_per_display_prefs = true;
         break;
       }