Optimize writes upon ProfileManager::UpdateLastUser.

BUG=481721

Review URL: https://codereview.chromium.org/1106213003

Cr-Commit-Position: refs/heads/master@{#327498}

chrome/browser/profiles/profile_info_cache.cc

@@ -471,6 +471,11 @@ size_t ProfileInfoCache::GetAvatarIconIndexOfProfileAtIndex(size_t index)
 }
 
 void ProfileInfoCache::SetProfileActiveTimeAtIndex(size_t index) {
+  if (base::Time::Now() - GetProfileActiveTimeAtIndex(index) <
+      base::TimeDelta::FromHours(1)) {
+    return;
+  }
+
   scoped_ptr<base::DictionaryValue> info(
       GetInfoForProfileAtIndex(index)->DeepCopy());
   info->SetDouble(kActiveTimeKey, base::Time::Now().ToDoubleT());

chrome/browser/profiles/profile_manager.cc

@@ -1332,8 +1332,10 @@ void ProfileManager::UpdateLastUser(Profile* last_active) {
   DCHECK(local_state);
   // Only keep track of profiles that we are managing; tests may create others.
   if (profiles_info_.find(last_active->GetPath()) != profiles_info_.end()) {
-    local_state->SetString(prefs::kProfileLastUsed,
-                           last_active->GetPath().BaseName().MaybeAsASCII());
+    std::string profile_path_base =
+        last_active->GetPath().BaseName().MaybeAsASCII();
+    if (profile_path_base != local_state->GetString(prefs::kProfileLastUsed))
+      local_state->SetString(prefs::kProfileLastUsed, profile_path_base);
 
     ProfileInfoCache& cache = GetProfileInfoCache();
     size_t profile_index =