Use the pinch viewport offset for tap disambiguation.

public/web/WebViewClient.h

Index: public/web/WebViewClient.h
diff --git a/public/web/WebViewClient.h b/public/web/WebViewClient.h
index d71c1a9b40f20020876272baae53a8533962ac0d..10c1ac4a232b59ce07c2cda0f9965b291429b985 100644
--- a/public/web/WebViewClient.h
+++ b/public/web/WebViewClient.h
@@ -204,9 +204,15 @@ public:
     // unless the view did not need a layout.
     virtual void didUpdateLayout() { }
 
+    // FIXME: This is a deprecated method. Remove it after the chromium change
+    // that uses the second didTapMultipleTargets() propagates.
+    //
     // Return true to swallow the input event if the embedder will start a disambiguation popup
     virtual bool didTapMultipleTargets(const WebGestureEvent&, const WebVector<WebRect>& targetRects) { return false; }
 
+    // Return true to swallow the input event if the embedder will start a disambiguation popup
+    virtual bool didTapMultipleTargets(const WebSize& pinchViewportOffset, const WebRect& touchRect, const WebVector<WebRect>& targetRects) { return false; }
+
     // Returns comma separated list of accept languages.
     virtual WebString acceptLanguages() { return WebString(); }