Migrate HostZoomMap to live in StoragePartition.

chrome/browser/ui/toolbar/wrench_menu_model.cc

Index: chrome/browser/ui/toolbar/wrench_menu_model.cc
diff --git a/chrome/browser/ui/toolbar/wrench_menu_model.cc b/chrome/browser/ui/toolbar/wrench_menu_model.cc
index f3b37f410f2b98865d02b91b0ea01922f5dd8419..8bfd159321490c7b9fc16e356631bc1164cd1ff6 100644
--- a/chrome/browser/ui/toolbar/wrench_menu_model.cc
+++ b/chrome/browser/ui/toolbar/wrench_menu_model.cc
@@ -78,7 +78,6 @@
 #endif
 
 using base::UserMetricsAction;
-using content::HostZoomMap;
 using content::WebContents;
 
 namespace {
@@ -285,6 +284,9 @@ WrenchMenuModel::WrenchMenuModel(ui::AcceleratorProvider* provider,
   Build();
   UpdateZoomControls();
 
+  // By asking for the HostZoomMap via the BrowserContext, we get the map
+  // associated with the default storage partition, and not the one related
+  // to any specialized storage partitions, e.g. those used by WebViewGuests.
   content_zoom_subscription_ = content::HostZoomMap::GetForBrowserContext(
       browser->profile())->AddZoomLevelChangedCallback(
           base::Bind(&WrenchMenuModel::OnZoomLevelChanged,