Introduce HostID and de-couple Extensions from "script injection System" [browser side]

chrome/browser/extensions/declarative_user_script_manager.cc

 // Copyright 2014 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/extensions/declarative_user_script_manager.h"
 
 #include "chrome/browser/extensions/declarative_user_script_master.h"
+#include "chrome/browser/profiles/profile.h"
+#include "extensions/browser/extension_registry.h"
 
 namespace extensions {
 
 DeclarativeUserScriptManager::DeclarativeUserScriptManager(Profile* profile)
-    : profile_(profile) {
+    : profile_(profile), extension_registry_observer_(this) {
+  extension_registry_observer_.Add(ExtensionRegistry::Get(profile));
 }
 
 DeclarativeUserScriptManager::~DeclarativeUserScriptManager() {
 }
 
 DeclarativeUserScriptMaster*
 DeclarativeUserScriptManager::GetDeclarativeUserScriptMasterByID(
-    const std::string& id) {
-  UserScriptMasterMap::iterator it = declarative_user_script_masters_.find(id);
+    const ConsumerID& consumer_id) {

[Devlin, 2015/01/21 23:25:20]

Thinking about this more, this means that every time a webui or extension
requests a declarative script, we create a new DeclarativeUserScriptMaster,
right?  Wouldn't it be better to only create one per extension/webui?

[Xi Han, 2015/01/22 17:19:36]

This is a good point, and I realize that the current implementation does
something different with my initial thoughts. I plan to create one per
extension/<webview>(no matter created by extensions or webUI). This keeps
consistent with existing code: all the declarative user scripts created by an
extension itself still share the same master, while scripts created by a
<webview> will have a master per <webview>. 

One solution is to update the way of assigning masters, but I think a better way
to do this is to change the way when creating new ConsumerID for declarative
user scripts:
1) if created by extensions itself: instance_id = a specified id, like
kDefaultDeclarativeInstanceID; compared with kDefaultStaticInstanceID for static
user scripts.
2) if created by <webview> : instance_id = GetNextId().

Using this way to create ConsumerID keeps the behaviors of content scripts
injection for extensions unchanged in everywhere.

+  UserScriptMasterMap::iterator it =
+      declarative_user_script_masters_.find(consumer_id);
 
   if (it != declarative_user_script_masters_.end())
     return it->second.get();
 
+  return CreateDeclarativeUserScriptMaster(consumer_id);
+}
+
+DeclarativeUserScriptMaster*
+DeclarativeUserScriptManager::CreateDeclarativeUserScriptMaster(
+    const ConsumerID& consumer_id) {
   linked_ptr<DeclarativeUserScriptMaster> master(
-      new DeclarativeUserScriptMaster(profile_, id));
-  declarative_user_script_masters_[id] = master;
+      new DeclarativeUserScriptMaster(profile_, consumer_id));
+  declarative_user_script_masters_[consumer_id] = master;
   return master.get();
 }
 
-}  // extensions
+void DeclarativeUserScriptManager::OnExtensionUnloaded(
+    content::BrowserContext* browser_context,
+    const Extension* extension,
+    UnloadedExtensionInfo::Reason reason) {
+  for (const auto& val : declarative_user_script_masters_) {
+    DeclarativeUserScriptMaster* master = val.second.get();
+    if (master->consumer_id().host_id() == extension->id())
+      master->ClearScripts();
+  }
+}
+
+}  // namespace extensions