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

chrome/browser/chromeos/login/signin/merge_session_load_page.cc

Index: chrome/browser/chromeos/login/signin/merge_session_load_page.cc
diff --git a/chrome/browser/chromeos/login/signin/merge_session_load_page.cc b/chrome/browser/chromeos/login/signin/merge_session_load_page.cc
index 33292fc5b9d3cb1d774e55deba011a512a47ef78..dbf11c280d48a62cd3f123a0c1ca6f3a86602bb9 100644
--- a/chrome/browser/chromeos/login/signin/merge_session_load_page.cc
+++ b/chrome/browser/chromeos/login/signin/merge_session_load_page.cc
@@ -24,6 +24,7 @@
 #include "chrome/grit/browser_resources.h"
 #include "chrome/grit/generated_resources.h"
 #include "content/public/browser/browser_thread.h"
+#include "content/public/browser/host_zoom_map.h"
 #include "content/public/browser/interstitial_page.h"
 #include "content/public/browser/notification_types.h"
 #include "content/public/browser/web_contents.h"
@@ -100,6 +101,10 @@ void MergeSessionLoadPage::OverrideRendererPrefs(
       content::RendererPreferences* prefs) {
   Profile* profile = Profile::FromBrowserContext(
       web_contents_->GetBrowserContext());
+  // TODO(wjmaclean): Convert this to use the HostZoomMap for the WebContents
+  // when HostZoomMap moves to StoragePartition.
+  prefs->default_zoom_level = content::HostZoomMap::GetDefaultForBrowserContext(
+                                  profile)->GetDefaultZoomLevel();
   renderer_preferences_util::UpdateFromSystemSettings(prefs, profile);
 }