Allow AppSearchProvider to provide recommendations.

chrome/browser/ui/app_list/search/app_result.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/app_list/search/app_result.h"
 
+#include "base/time/time.h"
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/browser/extensions/extension_util.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/app_list/app_context_menu.h"
 #include "chrome/browser/ui/app_list/app_list_controller_delegate.h"
 #include "chrome/browser/ui/app_list/search/tokenized_string.h"
 #include "chrome/browser/ui/app_list/search/tokenized_string_match.h"
 #include "chrome/browser/ui/extensions/extension_enable_flow.h"
 #include "chrome/browser/ui/webui/ntp/core_app_launcher_handler.h"
 #include "content/public/browser/user_metrics.h"
@@ skipping 49 matching lines @@
   Tags tags;
   tags.reserve(hits.size());
   for (size_t i = 0; i < hits.size(); ++i)
     tags.push_back(Tag(Tag::MATCH, hits[i].start(), hits[i].end()));
 
   set_title(title.text());
   set_title_tags(tags);
   set_relevance(match.relevance());
 }
 
+void AppResult::UpdateFromLastLaunched(const base::Time& last_launched) {
+  base::TimeDelta delta = base::Time::Now() - last_launched;
+  DCHECK_LE(0, delta.InSeconds());
+  const int kSecondsInWeek = 60 * 60 * 24 * 7;
+
+  // Set the relevance to a value between 0 and 1. This function decays as the
+  // time delta increases and reaches a value of 0.5 at 1 week.
+  set_relevance(1 / (1 + delta.InSecondsF() / kSecondsInWeek));

[Matt Giuca, 2014/07/22 04:31:07]

Why does the relevance have to be a float? How ingrained is this in the system?
It would be a lot simpler if the relevance could simply be a 64-bit integer.
Then you could just use last_launched.ToInternalValue() as the relevance (higher
is better), and not have to deal with Time::Now(), weeks, floats, or
reciprocals. (See my concerns later in the tests.)

[calamity, 2014/07/22 07:24:04]

Very. Boost values are +1-4 which rely on the base relevance to be 0-1 so all
other providers give relevances in the range 0-1.

[Matt Giuca, 2014/07/23 01:53:18]

Acknowledged.

+}
+
 void AppResult::Open(int event_flags) {
   const extensions::Extension* extension =
       extensions::ExtensionSystem::Get(profile_)->extension_service()
           ->GetInstalledExtension(app_id_);
   if (!extension)
     return;
 
   // Don't auto-enable apps that cannot be launched.
   if (!extensions::util::IsAppLaunchable(app_id_, profile_))
     return;
@@ skipping 112 matching lines @@
 
   NotifyItemUninstalled();
 }
 
 void AppResult::OnShutdown(extensions::ExtensionRegistry* registry) {
   DCHECK_EQ(extension_registry_, registry);
   StopObservingExtensionRegistry();
 }
 
 }  // namespace app_list