Keep the app list start page isolated from the browser's default zoom.

chrome/browser/ui/app_list/start_page_service.cc

 // Copyright 2013 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/ui/app_list/start_page_service.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/memory/singleton.h"
 #include "base/metrics/user_metrics.h"
 #include "base/prefs/pref_service.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/media/media_stream_infobar_delegate.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/search/hotword_service.h"
 #include "chrome/browser/search/hotword_service_factory.h"
 #include "chrome/browser/ui/app_list/recommended_apps.h"
 #include "chrome/browser/ui/app_list/speech_auth_helper.h"
 #include "chrome/browser/ui/app_list/speech_recognizer.h"
 #include "chrome/browser/ui/app_list/start_page_observer.h"
 #include "chrome/browser/ui/app_list/start_page_service_factory.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/url_constants.h"
+#include "components/ui/zoom/zoom_controller.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/notification_details.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_source.h"
 #include "content/public/browser/speech_recognition_session_preamble.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_contents_delegate.h"
 #include "extensions/browser/extension_system_provider.h"
@@ skipping 402 matching lines @@
 void StartPageService::Shutdown() {
   UnloadContents();
 #if defined(OS_CHROMEOS)
   audio_status_.reset();
 #endif
 
   speech_auth_helper_.reset();
   network_change_observer_.reset();
 }
 
+// Set the zoom level in DidNavigateMainFrame, as this is the earliest point
+// at which it can be done and not be affected by the ZoomController's
+// DidNavigateMainFrame handler.

[Matt Giuca, 2015/01/20 07:15:01]

Weird place for a comment (don't usually document overrides). Can you just put
it inside?

[benwells, 2015/01/20 07:31:09]

Done.

+void StartPageService::DidNavigateMainFrame(
+    const content::LoadCommittedDetails& /* details */,
+    const content::FrameNavigateParams& /* params */ ) {

[Matt Giuca, 2015/01/20 07:15:01]

Nit: No spaces in between the /* and */ (see style guide).

[benwells, 2015/01/20 07:31:09]

Done.

+  // Use a temporary zoom level for this web contents (aka isolated zoom
+  // mode) so changes to its zoom aren't reflected in any preferences.
+  ui_zoom::ZoomController::FromWebContents(contents_.get())->SetZoomMode(
+      ui_zoom::ZoomController::ZOOM_MODE_ISOLATED);
+  // Set to have a zoom level of '0', which corresponds to 100%, so the

[Matt Giuca, 2015/01/20 07:15:01]

Nit: Remove quotes around '0' (it is a number, not a char).

[benwells, 2015/01/20 07:31:09]

Done.

+  // contents aren't affected by the browser's default zoom level.
+  ui_zoom::ZoomController::FromWebContents(contents_.get())->SetZoomLevel(0);
+}
+
 void StartPageService::WebUILoaded() {
   // There's a race condition between the WebUI loading, and calling its JS
   // functions. Specifically, calling LoadContents() doesn't mean that the page
   // has loaded, but several code paths make this assumption. This function
   // allows us to defer calling JS functions until after the page has finished
   // loading.
   webui_finished_loading_ = true;
   for (const auto& cb : pending_webui_callbacks_)
     cb.Run();
   pending_webui_callbacks_.clear();
 }
 
 void StartPageService::LoadContents() {
   contents_.reset(content::WebContents::Create(
       content::WebContents::CreateParams(profile_)));
   contents_delegate_.reset(new StartPageWebContentsDelegate());
   contents_->SetDelegate(contents_delegate_.get());
 
+  // The ZoomController needs to be created before the web contents is observed
+  // by this object. Otherwise it will react to DidNavigateMainFrame after this
+  // object does, resetting the zoom mode in the process.
+  ui_zoom::ZoomController::CreateForWebContents(contents_.get());
+  Observe(contents_.get());
+
   contents_->GetController().LoadURL(
       GURL(chrome::kChromeUIAppListStartPageURL),
       content::Referrer(),
       ui::PAGE_TRANSITION_AUTO_TOPLEVEL,
       std::string());
 }
 
 void StartPageService::UnloadContents() {
   contents_.reset();

[Matt Giuca, 2015/01/20 07:15:01]

I think you need to add:
Observe(nullptr);

BEFORE this line --- otherwise you will have a dangling pointer to the deleted
contents_.

[benwells, 2015/01/20 07:31:09]

I don't think it's needed. See
https://code.google.com/p/chromium/codesearch#chromium/src/content/browser/we...
and also
https://code.google.com/p/chromium/codesearch#chromium/src/content/public/bro....

[Matt Giuca, 2015/01/20 22:39:23]

That removes the pointers from the WebContents to this WebContentsObserver, but
there is still a raw pointer from this WebContentsObserver back to the
now-deleted WebContents (WebContentsObserver::web_contents_).
Ah, I didn't know about ResetWebContents: looks like that is exactly equivalent
to Observe(nullptr) which I suggested. But it isn't being called from anywhere
as far as I can tell (contents_.reset() is resetting the scoped_ptr, not calling
WebContentsObserver::ResetWebContents).

So yeah, I still think you need to call ResetWebContents() explicitly (do that
instead of more awkwardly calling Observe(nullptr) which I previously
suggested), before contents_.reset().

[Matt Giuca, 2015/01/21 00:08:38]

Oops, as discussed offline, the WebContents destructor calls
WebContentsObserver::ResetWebContents so this is not needed here.

my bad

   webui_finished_loading_ = false;
 }
 
 }  // namespace app_list