Refactor extension handling code from AppShimHost into ExtensionAppShimHandler.

apps/app_shim/app_shim_handler_mac.cc

Index: apps/app_shim/app_shim_handler_mac.cc
diff --git a/apps/app_shim/app_shim_handler_mac.cc b/apps/app_shim/app_shim_handler_mac.cc
index 18cca9242674fbf4a19bb1d1d65e7704234e3bfe..54a45b73c4e9102452b65e76ba74ad13e34cbbed 100644
--- a/apps/app_shim/app_shim_handler_mac.cc
+++ b/apps/app_shim/app_shim_handler_mac.cc
@@ -25,7 +25,7 @@ class AppShimHandlerRegistry {
     if (it != handlers_.end())
       return it->second;
 
-    return NULL;
+    return default_handler_;
   }
 
   bool SetForAppMode(const std::string& app_mode_id, AppShimHandler* handler) {
@@ -36,14 +36,21 @@ class AppShimHandlerRegistry {
     return inserted_or_removed;
   }
 
+  bool SetDefaultHandler(AppShimHandler* handler) {
+    AppShimHandler* old_default_handler = default_handler_;

[tapted, 2013/05/21 06:15:37]

I think we can omit the return and add an appropriate DCHECK. (SetForAppMode has
a return so the compiler doesn't complain about inserted_or_removed being unused
when DCHECK is a no-op in Release builds.. -- and that DCHECK actually helped
diagnose some strangeness).

`DCHECK_NE(!default_handler_, !handler)` would do the job, but might be too
terse/obscure. Maybe DCHECK_NE(default_handler_ == NULL, handler == NULL)

[jackhou1, 2013/05/22 23:54:44]

Done.

+    default_handler_ = handler;
+    return default_handler_ == old_default_handler;
+  }
+
  private:
   friend struct DefaultSingletonTraits<AppShimHandlerRegistry>;
   typedef std::map<std::string, AppShimHandler*> HandlerMap;
 
-  AppShimHandlerRegistry() {}
+  AppShimHandlerRegistry() : default_handler_(NULL) {}
   ~AppShimHandlerRegistry() {}
 
   HandlerMap handlers_;
+  AppShimHandler* default_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(AppShimHandlerRegistry);
 };
@@ -67,4 +74,9 @@ AppShimHandler* AppShimHandler::GetForAppMode(const std::string& app_mode_id) {
   return AppShimHandlerRegistry::GetInstance()->GetForAppMode(app_mode_id);
 }
 
+// static
+void AppShimHandler::SetDefaultHandler(AppShimHandler* handler) {
+  AppShimHandlerRegistry::GetInstance()->SetDefaultHandler(handler);
+}
+
 }  // namespace apps