Add a histogram for tracking web store promo

chrome/common/extensions/extension_constants.h

Index: chrome/common/extensions/extension_constants.h
diff --git a/chrome/common/extensions/extension_constants.h b/chrome/common/extensions/extension_constants.h
index 332f386d5eb8901c21932c156a0fc9a49baca836..a32231eb28536394c32d017faa3677b60927a99e 100644
--- a/chrome/common/extensions/extension_constants.h
+++ b/chrome/common/extensions/extension_constants.h
@@ -239,6 +239,18 @@ namespace extension_misc {
     LAUNCH_PANEL,
     LAUNCH_TAB
   };
+
+  // The name of the apps promo histogram.
+  extern const char* kAppsPromoHistogram;
+
+  // The buckets used in the apps promo histogram.
+  enum AppsPromoBuckets {
+    PROMO_LAUNCH_APP,
+    PROMO_LAUNCH_WEB_STORE,
+    PROMO_CLOSE,
+    PROMO_EXPIRE,
+    PROMO_BUCKET_BOUNDARY = PROMO_EXPIRE + 1
+  };
 }  // extension_misc
 
 #endif  // CHROME_COMMON_EXTENSIONS_EXTENSION_CONSTANTS_H_