[Extensions] Refactor ExtensionContextMenuApiTest

This CL refactors ExtensionContextMenuApiTest.
ExtensionContextMenuApiTest's functions and member variables related to
visibility testing are moved to ExtensionContextMenuVisibilityApiTest. Furthermore, ExtensionApiTest.ContextMenus is divided to four tests and is moved to ExtensionContextMenuVisibilityApiTest.

Bug: 1093066
Change-Id: I6142790b01b583eb6664712d1fb1ab7df08452de
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2468346Reviewed-by: David Bertoni <dbertoni@chromium.org>
Commit-Queue: Ghazale Hosseinabadi <ghazale@chromium.org>
Cr-Commit-Position: refs/heads/master@{#817726}

chrome/browser/extensions/context_menu_matcher.h

@@ -71,6 +71,10 @@ class ContextMenuMatcher {
     is_smart_text_selection_enabled_ = enabled;
   }
 
+  const std::map<int, extensions::MenuItem::Id> extension_item_map() {
+    return extension_item_map_;
+  }
+
   bool IsCommandIdChecked(int command_id) const;
   bool IsCommandIdVisible(int command_id) const;
   bool IsCommandIdEnabled(int command_id) const;
@@ -81,7 +85,6 @@ class ContextMenuMatcher {
 
  private:
   friend class ::ExtensionContextMenuBrowserTest;
-  friend class ExtensionContextMenuApiTest;
 
   bool GetRelevantExtensionTopLevelItems(
       const MenuItem::ExtensionKey& extension_key,