Support multi-button press for synthetic mouse events

content/browser/renderer_host/input/synthetic_mouse_driver.h

Index: content/browser/renderer_host/input/synthetic_mouse_driver.h
diff --git a/content/browser/renderer_host/input/synthetic_mouse_driver.h b/content/browser/renderer_host/input/synthetic_mouse_driver.h
index 04a00706411073078cb8d139222fbcb118918cf8..95f12f2016e345e93438eaed9f621521b677f223 100644
--- a/content/browser/renderer_host/input/synthetic_mouse_driver.h
+++ b/content/browser/renderer_host/input/synthetic_mouse_driver.h
@@ -20,15 +20,17 @@ class CONTENT_EXPORT SyntheticMouseDriver : public SyntheticPointerDriver {
   void DispatchEvent(SyntheticGestureTarget* target,
                      const base::TimeTicks& timestamp) override;
 
-  void Press(float x, float y, int index = 0) override;
+  void Press(float x, float y, int index = 0, int button = 0) override;
   void Move(float x, float y, int index = 0) override;
-  void Release(int index = 0) override;
+  void Release(int index = 0, int button = 0) override;
 
   bool UserInputCheck(
       const SyntheticPointerActionParams& params) const override;
 
  private:
   blink::WebMouseEvent mouse_event_;
+  unsigned last_modifiers_;
+
   DISALLOW_COPY_AND_ASSIGN(SyntheticMouseDriver);
 };