[ImportantSites] Adding usage metrics.

chrome/browser/android/preferences/pref_service_bridge.cc

Index: chrome/browser/android/preferences/pref_service_bridge.cc
diff --git a/chrome/browser/android/preferences/pref_service_bridge.cc b/chrome/browser/android/preferences/pref_service_bridge.cc
index 44aaeb0e8dbd33e9d4cc96494c285f489ec4aa7f..985b7d0ba95510c6c67b6c16032be71c2bc99c0d 100644
--- a/chrome/browser/android/preferences/pref_service_bridge.cc
+++ b/chrome/browser/android/preferences/pref_service_bridge.cc
@@ -71,6 +71,8 @@ using base::android::ScopedJavaGlobalRef;
 using content::BrowserThread;
 
 namespace {
+
+// This should never change, as it's used for UMA metrics.

[Mark P, 2016/06/30 05:29:09]

You don't need this warning.  The problem I envisioned had to do with it
changing during a single session.  If it changes between sessions (say, during a
binary update), that's fine.

[dmurph, 2016/06/30 20:16:29]

Ah, ok.

 const size_t kMaxImportantSites = 5;
 
 Profile* GetOriginalProfile() {
@@ -683,6 +685,7 @@ static void FetchImportantSites(JNIEnv* env,
       env, java_callback.obj(), java_domains.obj(), java_origins.obj());
 }
 
+// This should never return a different constant, as it's used for UMA metrics.

[Mark P, 2016/06/30 05:29:09]

more correct:
// This value should no change during a sessions, as it's used for UMA metrics.

[dmurph, 2016/06/30 20:16:29]

Done.

 static jint GetMaxImportantSites(JNIEnv* env,
                                  const JavaParamRef<jclass>& clazz) {
   return kMaxImportantSites;