Update documentation of extension vs. app types

extensions/common/extension.h

 // Copyright (c) 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.
 
 #ifndef EXTENSIONS_COMMON_EXTENSION_H_
 #define EXTENSIONS_COMMON_EXTENSION_H_
 
 #include <map>
 #include <memory>
 #include <set>
@@ skipping 306 matching lines @@
   bool may_be_untrusted() const {
     return (creation_flags_ & MAY_BE_UNTRUSTED) != 0;
   }
   bool was_installed_by_default() const {
     return (creation_flags_ & WAS_INSTALLED_BY_DEFAULT) != 0;
   }
   bool was_installed_by_oem() const {
     return (creation_flags_ & WAS_INSTALLED_BY_OEM) != 0;
   }
 
-  // Type-related queries.
+  // Type-related queries. These are all mutually exclusive.
+  //
+  // The differences between the types of Extension are documented here:
+  // https://chromium.googlesource.com/chromium/src/+/HEAD/extensions/docs/extension_and_app_types.md
+  bool is_platform_app() const;         // aka "V2 app", "V2 packaged app"
+  bool is_hosted_app() const;           // Hosted app (or bookmark app)
+  bool is_legacy_packaged_app() const;  // aka "V1 packaged app"
+  bool is_extension() const;            // Regular browser extension, not an app
+  bool is_shared_module() const;        // Shared module
+  bool is_theme() const;                // Theme
+
+  // True if this is a platform app, hosted app, or legacy packaged app.
   bool is_app() const;
-  bool is_platform_app() const;
-  bool is_hosted_app() const;
-  bool is_legacy_packaged_app() const;
-  bool is_extension() const;
-  bool is_shared_module() const;
-  bool is_theme() const;
 
   void AddWebExtentPattern(const URLPattern& pattern);
   const URLPatternSet& web_extent() const { return extent_; }
 
  private:
   friend class base::RefCountedThreadSafe<Extension>;
 
   // Chooses the extension ID for an extension based on a variety of criteria.
   // The chosen ID will be set in |manifest|.
   static bool InitExtensionID(extensions::Manifest* manifest,
@@ skipping 210 matching lines @@
   const PermissionSet& permissions;
 
   UpdatedExtensionPermissionsInfo(const Extension* extension,
                                   const PermissionSet& permissions,
                                   Reason reason);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_EXTENSION_H_