[Extensions] Observe unloading extensions in the TabHelper

chrome/browser/extensions/tab_helper.cc

Index: chrome/browser/extensions/tab_helper.cc
diff --git a/chrome/browser/extensions/tab_helper.cc b/chrome/browser/extensions/tab_helper.cc
index 67fd240c883c4dd761db88f9da40670cdf557817..bc5ecd91f614ec65576c396aa593ed65d18bb456 100644
--- a/chrome/browser/extensions/tab_helper.cc
+++ b/chrome/browser/extensions/tab_helper.cc
@@ -84,6 +84,7 @@ TabHelper::TabHelper(content::WebContents* web_contents)
       location_bar_controller_(new LocationBarController(web_contents)),
       extension_action_runner_(new ExtensionActionRunner(web_contents)),
       webstore_inline_installer_factory_(new WebstoreInlineInstallerFactory()),
+      registry_observer_(this),
       image_loader_ptr_factory_(this),
       weak_ptr_factory_(this) {
   // The ActiveTabPermissionManager requires a session ID; ensure this
@@ -169,6 +170,11 @@ void TabHelper::SetExtensionApp(const Extension* extension) {
 
   extension_app_ = extension;
 
+  if (extension_app_) {

[lazyboy, 2016/06/03 01:43:56]

lgtm given this is not true:
Is it possible that two extensions get associated with the same TabHelper?
SetExtensionApp(extension1)
SetExtensionApp(extension2)
Uninstall -> extension 2
Uninstall -> extension 1, the DCHECK in line 545 below will fail.

[Devlin, 2016/06/06 16:50:22]

That flow might be able to happen (if e.g. you navigate from one hosted app to
another), but that shouldn't trigger the DCHECK:
SetExtensionApp(extension1) -> register observer, extension_app_ = extension1
SetExtensionApp(extension2) -> extension_app_ = extension2
Uninstall(extension2) -> extension_app_ = nullptr, unregister observer
Uninstall(extension1) -> since unregistered, never see notification

However, a similar flow would cause a DCHECK:
SetExtensionApp(extension1)
SetExtensionApp(nullptr)
Uninstall(extension1)

I've add logic to SetExtensionApp() to remove the observer if setting to nullptr
to address it.

[lazyboy, 2016/06/06 18:10:49]

Acknowledged.

+    registry_observer_.Add(
+        ExtensionRegistry::Get(web_contents()->GetBrowserContext()));
+  }
+
   UpdateExtensionAppIcon(extension_app_);
 
   content::NotificationService::current()->Notify(
@@ -532,6 +538,17 @@ WebContents* TabHelper::GetAssociatedWebContents() const {
   return web_contents();
 }
 
+void TabHelper::OnExtensionUnloaded(
+    content::BrowserContext* browser_context,
+    const Extension* extension,
+    UnloadedExtensionInfo::Reason reason) {
+  DCHECK(extension_app_);
+  if (extension == extension_app_) {
+    SetExtensionApp(nullptr);
+    registry_observer_.RemoveAll();
+  }
+}
+
 void TabHelper::GetApplicationInfo(WebAppAction action) {
   NavigationEntry* entry =
       web_contents()->GetController().GetLastCommittedEntry();