Introduce ChromeZoomLevelPref, make zoom level prefs independent of profile prefs.

chrome/browser/chromeos/login/ui/webui_login_view.cc

Index: chrome/browser/chromeos/login/ui/webui_login_view.cc
diff --git a/chrome/browser/chromeos/login/ui/webui_login_view.cc b/chrome/browser/chromeos/login/ui/webui_login_view.cc
index 42febae6d6b1cb088d26abe058069b3217ad0aee..97cd86a9f8d80e1656286e134660ca488e0c3f96 100644
--- a/chrome/browser/chromeos/login/ui/webui_login_view.cc
+++ b/chrome/browser/chromeos/login/ui/webui_login_view.cc
@@ -32,12 +32,14 @@
 #include "chromeos/network/network_state_handler.h"
 #include "components/password_manager/core/browser/password_manager.h"
 #include "components/web_modal/web_contents_modal_dialog_manager.h"
+#include "content/public/browser/host_zoom_map.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/render_frame_host.h"
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/render_widget_host_view.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_ui.h"
+#include "content/public/common/renderer_preferences.h"
 #include "third_party/WebKit/public/web/WebInputEvent.h"
 #include "ui/gfx/rect.h"
 #include "ui/gfx/size.h"
@@ -200,9 +202,12 @@ void WebUILoginView::Init() {
   extensions::ChromeExtensionWebContentsObserver::CreateForWebContents(
       web_contents);
   WebContentsObserver::Observe(web_contents);
-  renderer_preferences_util::UpdateFromSystemSettings(
-      web_contents->GetMutableRendererPrefs(),
-      signin_profile);
+  content::RendererPreferences* prefs = web_contents->GetMutableRendererPrefs();
+  renderer_preferences_util::UpdateFromSystemSettings(prefs, signin_profile);
+  // TODO(wjmaclean): Convert this to use the HostZoomMap for the WebContents
+  // when HostZoomMap moves to StoragePartition.
+  prefs->default_zoom_level = content::HostZoomMap::GetDefaultForBrowserContext(
+                                  signin_profile)->GetDefaultZoomLevel();
 }
 
 const char* WebUILoginView::GetClassName() const {