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..dca6d95cfaae4430caee580e71f198bb8723a715 100644
--- a/chrome/common/extensions/extension_constants.h
+++ b/chrome/common/extensions/extension_constants.h
@@ -239,6 +239,24 @@ 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
+  };
+
+  // The URL prefixes used by the NTP to signal when the web store or an app
+  // has launched. These are used for histogram purposes.
+  extern const char* kLaunchAppPingURL;
+  extern const char* kLaunchWebStorePingURL;
+
 }  // extension_misc
 
 #endif  // CHROME_COMMON_EXTENSIONS_EXTENSION_CONSTANTS_H_