Make installed_loader UMA less wasteful.

chrome/browser/extensions/installed_loader.cc

Index: chrome/browser/extensions/installed_loader.cc
diff --git a/chrome/browser/extensions/installed_loader.cc b/chrome/browser/extensions/installed_loader.cc
index ab16252f0df436508c00f4ed1db55d1644c44059..e8c557c8a500445c6254198af9206b2f400626a2 100644
--- a/chrome/browser/extensions/installed_loader.cc
+++ b/chrome/browser/extensions/installed_loader.cc
@@ -59,8 +59,9 @@ enum ManifestReloadReason {
 // long as existing values are not changed.
 enum BackgroundPageType {
   NO_BACKGROUND_PAGE = 0,
-  BACKGROUND_PAGE_PERSISTENT = 1,
-  EVENT_PAGE = 2,
+  BACKGROUND_PAGE_PERSISTENT,
+  EVENT_PAGE,
+  NUM_BACKGROUND_PAGE_TYPES
 };
 
 // Used in histogram Extensions.ExternalItemState. Values may be added, as
@@ -223,7 +224,8 @@ void InstalledLoader::LoadAllExtensions() {
     ManifestReloadReason reload_reason = ShouldReloadExtensionManifest(*info);
     ++reload_reason_counts[reload_reason];
     UMA_HISTOGRAM_ENUMERATION("Extensions.ManifestReloadEnumValue",
-                              reload_reason, 100);
+                              reload_reason,
+                              NUM_MANIFEST_RELOAD_REASONS);
 
     if (reload_reason != NOT_NEEDED) {
       // Reloading an extension reads files from disk.  We do this on the
@@ -316,13 +318,15 @@ void InstalledLoader::LoadAllExtensions() {
     // muck up any of the stats. Later, though, we want to omit component and
     // unpacked, as they are less interesting.
     if (extension->is_app())
-      UMA_HISTOGRAM_ENUMERATION("Extensions.AppLocation", location, 100);
+      UMA_HISTOGRAM_ENUMERATION(
+          "Extensions.AppLocation", location, Manifest::NUM_LOCATIONS);
     else if (extension->is_extension())
-      UMA_HISTOGRAM_ENUMERATION("Extensions.ExtensionLocation", location, 100);
+      UMA_HISTOGRAM_ENUMERATION(
+          "Extensions.ExtensionLocation", location, Manifest::NUM_LOCATIONS);
 
     if (!ManifestURL::UpdatesFromGallery(extension)) {
       UMA_HISTOGRAM_ENUMERATION(
-          "Extensions.NonWebstoreLocation", location, 100);
+          "Extensions.NonWebstoreLocation", location, Manifest::NUM_LOCATIONS);
 
       // Check for inconsistencies if the extension was supposedly installed
       // from the webstore.
@@ -378,13 +382,14 @@ void InstalledLoader::LoadAllExtensions() {
     if (type == Manifest::TYPE_EXTENSION) {
       UMA_HISTOGRAM_ENUMERATION("Extensions.BackgroundPageType",
                                 GetBackgroundPageType(extension),
-                                10);
+                                NUM_BACKGROUND_PAGE_TYPES);
     }
 
     // Using an enumeration shows us the total installed ratio across all users.
     // Using the totals per user at each startup tells us the distribution of
     // usage for each user (e.g. 40% of users have at least one app installed).
-    UMA_HISTOGRAM_ENUMERATION("Extensions.LoadType", type, 100);
+    UMA_HISTOGRAM_ENUMERATION(
+        "Extensions.LoadType", type, Manifest::NUM_LOAD_TYPES);
     switch (type) {
       case Manifest::TYPE_THEME:
         ++theme_count;