Block navigations in extensions via ShouldTransferNavigation (not via OpenURL).

chrome/browser/extensions/extension_view_host.cc

Index: chrome/browser/extensions/extension_view_host.cc
diff --git a/chrome/browser/extensions/extension_view_host.cc b/chrome/browser/extensions/extension_view_host.cc
index 615e13cd8abf6e28db278d05fbf2ccec1f60db9e..ea544c71fd365928d990663cee02277bf889e04e 100644
--- a/chrome/browser/extensions/extension_view_host.cc
+++ b/chrome/browser/extensions/extension_view_host.cc
@@ -165,6 +165,14 @@ WebContents* ExtensionViewHost::OpenURLFromTab(
   }
 }
 
+bool ExtensionViewHost::ShouldTransferNavigation(
+    bool is_main_frame_navigation) {
+  // Block navigations that cause main frame of an extension pop-up (or
+  // background page) to navigate to non-extension content (i.e. to web
+  // content).
+  return !is_main_frame_navigation;
+}
+
 bool ExtensionViewHost::PreHandleKeyboardEvent(
     WebContents* source,
     const NativeWebKeyboardEvent& event,