Add component for feature engagement tracking.

chrome/common/chrome_constants.cc

Index: chrome/common/chrome_constants.cc
diff --git a/chrome/common/chrome_constants.cc b/chrome/common/chrome_constants.cc
index c0eecffa54d7cd5b8c46a7c59a08ca776ba389bd..466f94d3b8f816a61178a9744d9c821857202fbd 100644
--- a/chrome/common/chrome_constants.cc
+++ b/chrome/common/chrome_constants.cc
@@ -144,6 +144,8 @@ const base::FilePath::CharType kExtensionActivityLogFilename[] =
     FPL("Extension Activity");
 const base::FilePath::CharType kExtensionsCookieFilename[] =
     FPL("Extension Cookies");
+const base::FilePath::CharType kFeatureEngagementTrackerStorageDirname[] =
+    FPL("Feature Engagement Tracker");
 const base::FilePath::CharType kFirstRunSentinel[] = FPL("First Run");
 const base::FilePath::CharType kGCMStoreDirname[] = FPL("GCM Store");
 const base::FilePath::CharType kLocalStateFilename[] = FPL("Local State");