Add a comment to ActivityName::activity_name.

components/arc/intent_helper/activity_icon_loader.h

 // Copyright 2016 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.
 
 #ifndef COMPONENTS_ARC_INTENT_HELPER_ACTIVITY_ICON_LOADER_H_
 #define COMPONENTS_ARC_INTENT_HELPER_ACTIVITY_ICON_LOADER_H_
 
 #include <map>
 #include <memory>
 #include <string>
@@ skipping 16 matching lines @@
   struct Icons {
     Icons(const gfx::Image& icon16, const gfx::Image& icon48);
     const gfx::Image icon16;  // 16 dip
     const gfx::Image icon48;  // 48 dip
   };
 
   struct ActivityName {
     ActivityName(const std::string& package_name,
                  const std::string& activity_name);
     bool operator<(const ActivityName& other) const;
+
     // TODO(yusukes): Add const to these variables later. At this point,
     // doing so seems to confuse g++ 4.6 on builders.
     std::string package_name;
+
+    // Can be empty. When |activity_name| is empty, the loader tries to fetch
+    // the package's default icon.
     std::string activity_name;
   };
 
   using ActivityToIconsMap = std::map<ActivityName, Icons>;
   using OnIconsReadyCallback =
       base::Callback<void(std::unique_ptr<ActivityToIconsMap>)>;
 
   ActivityIconLoader();
 
   // Removes icons associated with |package_name| from the cache.
@@ skipping 39 matching lines @@
   ActivityToIconsMap cached_icons_;
 
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(ActivityIconLoader);
 };
 
 }  // namespace arc
 
 #endif  // COMPONENTS_ARC_INTENT_HELPER_ACTIVITY_ICON_LOADER_H_