Revert of Remove deprecated extension notification from ProcessManager. (patchset #2 id:20001 of https://codereview.chromium.org/566863002/)

Reason for revert:
One of the tests crashes with a UAF: http://crbug.com/414245

Original issue's description:
> Remove deprecated extension notification from ProcessManager.
>
> This patch used EntensionRegistryObserver instead of DEPRECATED extension
> NOTIFICATION_EXTENSION_UNLOADED_DEPRECATED removed now.
>
> BUG=411568
>
> Committed: https://crrev.com/1bd52ffda33ffc5614dab8e3f3d677f0a528e763
> Cr-Commit-Position: refs/heads/master@{#294799}

TBR=bauerb@chromium.org,rockot@chromium.org,limasdf@gmail.com,jitendra.ks@samsung.com
NOTREECHECKS=true
NOTRY=true
BUG=411568

Review URL: https://codereview.chromium.org/570073002

Cr-Commit-Position: refs/heads/master@{#294806}

3 files changed, 46 insertions, 40 deletions

diff --git a/extensions/browser/process_manager.cc b/extensions/browser/process_manager.cc
index 38c476e..c3bcd50 100644
--- a/extensions/browser/process_manager.cc
+++ b/extensions/browser/process_manager.cc
@@ -247,11 +247,16 @@ ProcessManager::ProcessManager(BrowserContext* context,
       weak_ptr_factory_(this) {
   // ExtensionRegistry is shared between incognito and regular contexts.
   DCHECK_EQ(original_context, extension_registry_->browser_context());
-  extension_registry_->AddObserver(this);
   registrar_.Add(this,
                  extensions::NOTIFICATION_EXTENSIONS_READY_DEPRECATED,
                  content::Source<BrowserContext>(original_context));
   registrar_.Add(this,
+                 extensions::NOTIFICATION_EXTENSION_LOADED_DEPRECATED,
+                 content::Source<BrowserContext>(original_context));
+  registrar_.Add(this,
+                 extensions::NOTIFICATION_EXTENSION_UNLOADED_DEPRECATED,
+                 content::Source<BrowserContext>(original_context));
+  registrar_.Add(this,
                  extensions::NOTIFICATION_EXTENSION_HOST_DESTROYED,
                  content::Source<BrowserContext>(context));
   registrar_.Add(this,
@@ -286,7 +291,6 @@ ProcessManager::ProcessManager(BrowserContext* context,
 }
 
 ProcessManager::~ProcessManager() {
-  extension_registry_->RemoveObserver(this);
   CloseBackgroundHosts();
   DCHECK(background_hosts_.empty());
   content::DevToolsAgentHost::RemoveAgentStateCallback(devtools_callback_);
@@ -684,6 +688,33 @@ void ProcessManager::Observe(int type,
       break;
     }
 
+    case extensions::NOTIFICATION_EXTENSION_LOADED_DEPRECATED: {
+      BrowserContext* context = content::Source<BrowserContext>(source).ptr();
+      ExtensionSystem* system = ExtensionSystem::Get(context);
+      if (system->ready().is_signaled()) {
+        // The extension system is ready, so create the background host.
+        const Extension* extension =
+            content::Details<const Extension>(details).ptr();
+        CreateBackgroundHostForExtensionLoad(this, extension);
+      }
+      break;
+    }
+
+    case extensions::NOTIFICATION_EXTENSION_UNLOADED_DEPRECATED: {
+      const Extension* extension =
+          content::Details<UnloadedExtensionInfo>(details)->extension;
+      for (ExtensionHostSet::iterator iter = background_hosts_.begin();
+           iter != background_hosts_.end(); ++iter) {
+        ExtensionHost* host = *iter;
+        if (host->extension_id() == extension->id()) {
+          CloseBackgroundHost(host);
+          break;
+        }
+      }
+      UnregisterExtension(extension->id());
+      break;
+    }
+
     case extensions::NOTIFICATION_EXTENSION_HOST_DESTROYED: {
       ExtensionHost* host = content::Details<ExtensionHost>(details).ptr();
       if (background_hosts_.erase(host)) {
@@ -749,31 +780,6 @@ void ProcessManager::Observe(int type,
   }
 }
 
-void ProcessManager::OnExtensionLoaded(content::BrowserContext* browser_context,
-                                       const extensions::Extension* extension) {
-  ExtensionSystem* system = ExtensionSystem::Get(browser_context);
-  if (system->ready().is_signaled()) {
-    // The extension system is ready, so create the background host.
-    CreateBackgroundHostForExtensionLoad(this, extension);
-  }
-}
-
-void ProcessManager::OnExtensionUnloaded(
-    content::BrowserContext* browser_context,
-    const extensions::Extension* extension,
-    extensions::UnloadedExtensionInfo::Reason reason) {
-  for (ExtensionHostSet::iterator iter = background_hosts_.begin();
-       iter != background_hosts_.end();
-       ++iter) {
-    ExtensionHost* host = *iter;
-    if (host->extension_id() == extension->id()) {
-      CloseBackgroundHost(host);
-      break;
-    }
-  }
-  UnregisterExtension(extension->id());
-}
-
 void ProcessManager::OnDevToolsStateChanged(
     content::DevToolsAgentHost* agent_host,
     bool attached) {
diff --git a/extensions/browser/process_manager.h b/extensions/browser/process_manager.h
index 8de9bef..e7be995 100644
--- a/extensions/browser/process_manager.h
+++ b/extensions/browser/process_manager.h
@@ -17,7 +17,6 @@
 #include "base/time/time.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
-#include "extensions/browser/extension_registry_observer.h"
 #include "extensions/common/view_type.h"
 
 class GURL;
@@ -41,8 +40,7 @@ class ProcessManagerObserver;
 // Manages dynamic state of running Chromium extensions. There is one instance
 // of this class per Profile. OTR Profiles have a separate instance that keeps
 // track of split-mode extensions only.
-class ProcessManager : public content::NotificationObserver,
-                       public extensions::ExtensionRegistryObserver {
+class ProcessManager : public content::NotificationObserver {
  public:
   typedef std::set<extensions::ExtensionHost*> ExtensionHostSet;
   typedef ExtensionHostSet::const_iterator const_iterator;
@@ -180,16 +178,6 @@ class ProcessManager : public content::NotificationObserver,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
-  // extensions::ExtensionRegistryObserver:
-  virtual void OnExtensionLoaded(
-      content::BrowserContext* browser_context,
-      const extensions::Extension* extension) OVERRIDE;
-
-  virtual void OnExtensionUnloaded(
-      content::BrowserContext* browser_context,
-      const extensions::Extension* extension,
-      extensions::UnloadedExtensionInfo::Reason reason) OVERRIDE;
-
   content::NotificationRegistrar registrar_;
 
   // The set of ExtensionHosts running viewless background extensions.
diff --git a/extensions/browser/process_manager_unittest.cc b/extensions/browser/process_manager_unittest.cc
index 957e3a2..e04b0d3 100644
--- a/extensions/browser/process_manager_unittest.cc
+++ b/extensions/browser/process_manager_unittest.cc
@@ -111,6 +111,13 @@ TEST_F(ProcessManagerTest, ExtensionNotificationRegistration) {
                            extensions::NOTIFICATION_EXTENSIONS_READY_DEPRECATED,
                            original_context()));
   EXPECT_TRUE(IsRegistered(manager1.get(),
+                           extensions::NOTIFICATION_EXTENSION_LOADED_DEPRECATED,
+                           original_context()));
+  EXPECT_TRUE(
+      IsRegistered(manager1.get(),
+                   extensions::NOTIFICATION_EXTENSION_UNLOADED_DEPRECATED,
+                   original_context()));
+  EXPECT_TRUE(IsRegistered(manager1.get(),
                            extensions::NOTIFICATION_EXTENSION_HOST_DESTROYED,
                            original_context()));
 
@@ -124,6 +131,11 @@ TEST_F(ProcessManagerTest, ExtensionNotificationRegistration) {
   EXPECT_EQ(incognito_context(), manager2->GetBrowserContext());
   EXPECT_EQ(0u, manager2->background_hosts().size());
 
+  // Some notifications are observed for the original context.
+  EXPECT_TRUE(IsRegistered(manager2.get(),
+                           extensions::NOTIFICATION_EXTENSION_LOADED_DEPRECATED,
+                           original_context()));
+
   // Some notifications are observed for the incognito context.
   EXPECT_TRUE(IsRegistered(manager2.get(),
                            extensions::NOTIFICATION_EXTENSION_HOST_DESTROYED,