OverscrollController consumes scroll updates only during gesture-nav.

content/browser/renderer_host/overscroll_controller.h

Index: content/browser/renderer_host/overscroll_controller.h
diff --git a/content/browser/renderer_host/overscroll_controller.h b/content/browser/renderer_host/overscroll_controller.h
index 5577ce97f3d5893fc1076e87efcbdafaad3139c2..a6287efd3bd75571c49dba54c50076783e2d8488 100644
--- a/content/browser/renderer_host/overscroll_controller.h
+++ b/content/browser/renderer_host/overscroll_controller.h
@@ -91,8 +91,9 @@ class OverscrollController {
 
   // Processes horizontal overscroll. This can update both the overscroll mode
   // and the over scroll amount (i.e. |overscroll_mode_|, |overscroll_delta_x_|
-  // and |overscroll_delta_y_|).
-  void ProcessOverscroll(float delta_x,
+  // and |overscroll_delta_y_|). Returns true if overscroll was handled by the
+  // delegate.
+  bool ProcessOverscroll(float delta_x,
                          float delta_y,
                          blink::WebInputEvent::Type event_type);