Rename constants used with default apps to confrom with naming convention.

chrome/browser/extensions/extension_service.cc

Index: chrome/browser/extensions/extension_service.cc
===================================================================
--- chrome/browser/extensions/extension_service.cc	(revision 112974)
+++ chrome/browser/extensions/extension_service.cc	(working copy)
@@ -747,11 +747,11 @@
   UMA_HISTOGRAM_ENUMERATION("Extensions.ExtensionUninstalled", 1, 2);
 
   static bool default_apps_trial_exists =
-      base::FieldTrialList::TrialExists(kDefaultAppsTrial_Name);
+      base::FieldTrialList::TrialExists(kDefaultAppsTrialName);
   if (default_apps_trial_exists) {
     UMA_HISTOGRAM_ENUMERATION(
         base::FieldTrial::MakeName("Extensions.ExtensionUninstalled",
-                                   kDefaultAppsTrial_Name),
+                                   kDefaultAppsTrialName),
         1, 2);
   }