Take 2 at implementing activeTab.

chrome/browser/extensions/active_tab_permission_manager.cc

+// Copyright (c) 2012 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/active_tab_permission_manager.h"
+
+#include "base/memory/ref_counted.h"
+#include "chrome/browser/extensions/extension_tab_helper.h"
+#include "chrome/browser/extensions/extension_tab_util.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/ui/tab_contents/tab_contents_wrapper.h"
+#include "chrome/common/chrome_notification_types.h"
+#include "chrome/common/extensions/extension.h"
+#include "chrome/common/extensions/extension_messages.h"
+#include "chrome/common/extensions/extension_permission_set.h"
+#include "content/public/browser/navigation_entry.h"
+#include "content/public/browser/notification_details.h"
+#include "content/public/browser/notification_source.h"
+#include "content/public/browser/render_process_host.h"
+#include "content/public/browser/web_contents.h"
+
+using content::RenderProcessHost;
+using content::WebContentsObserver;
+
+namespace extensions {
+
+namespace {
+
+// Sends a copy of |message| to every RenderProcessHost in |profile|.
+template <class E>
+void SendToProfile(Profile* profile, const E& message) {

[Aaron Boodman, 2012/06/06 01:03:13]

Nit: this would make more sense me if it were named SendToRenderers.

[not at google - send to devlin, 2012/06/06 07:38:40]

Done.

+  for (RenderProcessHost::iterator i(RenderProcessHost::AllHostsIterator());
+       !i.IsAtEnd(); i.Advance()) {
+    RenderProcessHost* host = i.GetCurrentValue();
+    Profile* host_profile =
+        Profile::FromBrowserContext(host->GetBrowserContext());
+    if (host_profile->IsSameProfile(profile))
+      host->Send(new E(message));

[Aaron Boodman, 2012/06/06 01:03:13]

Is it possible to pass a heap-allocated message to SendToProfile to avoid this
copy?

[not at google - send to devlin, 2012/06/06 07:38:40]

Everybody always does "Send(new BlahMessage)" so I figured Send must take
ownership, so copying would be kind of unavoidable. Looking at ipc/ipc_message.h
there's no other way to do it.

+  }
+}
+
+}
+
+ActiveTabPermissionManager::ActiveTabPermissionManager(
+    TabContentsWrapper* tab_contents)
+    : WebContentsObserver(tab_contents->web_contents()),
+      tab_contents_(tab_contents) {
+  InsertActiveURL(web_contents()->GetURL());
+}
+
+ActiveTabPermissionManager::~ActiveTabPermissionManager() {}
+
+void ActiveTabPermissionManager::Grant(const Extension* extension) {
+  if (!extension->HasAPIPermission(ExtensionAPIPermission::kActiveTab))
+    return;
+
+  int tab_id = tab_contents_->extension_tab_helper()->GetTabId();
+
+  // Only need to check the number of permissions here rather than the URLs
+  // themselves, because the set can only ever grow.
+  const URLPatternSet* old_permissions =
+      extension->GetTabSpecificHostPermissions(tab_id);
+  if (old_permissions && old_permissions->size() == active_urls_.size())
+    return;
+
+  granted_.Insert(extension);

[Aaron Boodman, 2012/06/06 01:03:13]

What happens if the extension is unloaded?

[not at google - send to devlin, 2012/06/06 07:38:40]

The extension stays around cos it's refcounted, and when it's
re-enabled/installed it'll have the same ID so still have access to the tab.

When I wrote the code I thought about it and was like "eh yeah that sounds
right" but I don't know anymore. Listening to unloaded events now.

+  extension->SetTabSpecificHostPermissions(tab_id, active_urls_);
+  SendToProfile(
+      tab_contents_->profile(),
+      ExtensionMsg_SetTabSpecificPermissions(GetPageID() + 1, // mauahaha

[Aaron Boodman, 2012/06/06 01:03:13]

also, i believe the correct spelling is 'muah'. It's supposed to sound like
'mwuah', not 'mouh'.

[Aaron Boodman, 2012/06/06 01:03:13]

I don't follow... why +1?

[not at google - send to devlin, 2012/06/06 07:38:40]

Oh, I was just testing that the page ID blocking logic worked.  It does! 
Just... forgot to take it out.

+                                             tab_id,
+                                             extension->id(),
+                                             active_urls_));
+}
+
+void ActiveTabPermissionManager::DidCommitProvisionalLoadForFrame(
+    int64 frame_id,
+    bool is_main_frame,
+    const GURL& url,
+    content::PageTransition transition_type,
+    content::RenderViewHost* render_view_host) {
+  if (is_main_frame)
+    ClearActiveURLsAndNotify();
+  InsertActiveURL(url);
+}
+
+void ActiveTabPermissionManager::WebContentsDestroyed(
+    content::WebContents* web_contents) {
+  ClearActiveURLsAndNotify();
+}
+
+void ActiveTabPermissionManager::ClearActiveURLsAndNotify() {
+  active_urls_.ClearPatterns();
+
+  // The rest of this method deals with informing the extension(s) that the
+  // permissions for this tab need to be cleared. No need if there aren't any.
+  if (granted_.is_empty())
+    return;
+
+  int tab_id = tab_contents_->extension_tab_helper()->GetTabId();
+  std::vector<std::string> extension_ids;
+
+  for (ExtensionSet::const_iterator it = granted_.begin();
+       it != granted_.end(); ++it) {
+    (*it)->ClearTabSpecificHostPermissions(tab_id);
+    extension_ids.push_back((*it)->id());
+  }
+  granted_.Clear();
+
+  SendToProfile(
+      tab_contents_->profile(),
+      ExtensionMsg_ClearTabSpecificPermissions(tab_id, extension_ids));
+}
+
+void ActiveTabPermissionManager::InsertActiveURL(const GURL& url) {
+  URLPattern pattern(URLPattern::SCHEME_FILE |

[Aaron Boodman, 2012/06/06 01:03:13]

UserScript::kValidUserScriptSchemes? (ftp is a bit dubious, but at least it's
consistent).

[not at google - send to devlin, 2012/06/06 07:38:40]

Didn't know about that constant. Done.

+                     URLPattern::SCHEME_HTTP |
+                     URLPattern::SCHEME_HTTPS);
+  if (pattern.Parse(url.spec()) == URLPattern::PARSE_SUCCESS)
+    active_urls_.AddPattern(pattern);
+}
+
+int32 ActiveTabPermissionManager::GetPageID() {
+  return tab_contents_->web_contents()->GetController().GetActiveEntry()->
+      GetPageID();
+}
+
+}  // namespace extensions