Moved window opening callback to WebStateDelegate.

ios/web/public/web_state/web_state_delegate.h

Index: ios/web/public/web_state/web_state_delegate.h
diff --git a/ios/web/public/web_state/web_state_delegate.h b/ios/web/public/web_state/web_state_delegate.h
index 8eebecc4027ef0502a965f665f3b0b4396c8bf2a..01e189f6ddc7d26c6a5e26f172894586746b0b33 100644
--- a/ios/web/public/web_state/web_state_delegate.h
+++ b/ios/web/public/web_state/web_state_delegate.h
@@ -23,6 +23,16 @@ class WebStateDelegate {
  public:
   WebStateDelegate();
 
+  // Called when |source| wants to open a new window. |url| is the URL of
+  // the new window; |opener_url| is the URL of the page which requested a
+  // window to be open; |initiated_by_user| is true if action was caused by the
+  // user. |source| will not open a window if this method returns nil. This
+  // method can not return |source|.
+  virtual WebState* CreateNewWebState(WebState* source,
+                                      const GURL& url,
+                                      const GURL& opener_url,
+                                      bool initiated_by_user);
+
   // Returns the WebState the URL is opened in, or nullptr if the URL wasn't
   // opened immediately.
   virtual WebState* OpenURLFromWebState(WebState*,