Fire pointerup/down events for corresponding mouse events.

third_party/WebKit/Source/core/input/EventHandler.h

Index: third_party/WebKit/Source/core/input/EventHandler.h
diff --git a/third_party/WebKit/Source/core/input/EventHandler.h b/third_party/WebKit/Source/core/input/EventHandler.h
index 50611cef0bfd515b19af2a8793ba70bbcc270978..4b5a77f87f67fad295b1e2aa8d548d7f911ae156 100644
--- a/third_party/WebKit/Source/core/input/EventHandler.h
+++ b/third_party/WebKit/Source/core/input/EventHandler.h
@@ -283,7 +283,7 @@ private:
     void updateMouseEventTargetNode(Node*, const PlatformMouseEvent&);
 
     // Returns true when the sent PE has defaultPrevented or defaultHandled set.
-    bool dispatchPointerEventForMouseEvent(Node* target, const AtomicString& eventType, const PlatformMouseEvent&, Node* relatedTarget);
+    bool dispatchPointerEventForMouseEvent(Node* target, const AtomicString& eventType, const PlatformMouseEvent&, Node* relatedTarget = nullptr);
 
     // Dispatches mouseover, mouseout, mouseenter and mouseleave events to appropriate nodes when the mouse pointer moves from one node to another.
     void sendMouseEventsForNodeTransition(Node*, Node*, const PlatformMouseEvent&);
@@ -414,6 +414,11 @@ private:
 
     PointerIdManager m_pointerIdManager;
 
+    // Prevents firing mousedown, mousemove & mouseup in-between a canceled pointerdown and next pointerup/pointercancel.
+    // See "PREVENT MOUSE EVENT flag" in the spec:
+    //   https://w3c.github.io/pointerevents/#compatibility-mapping-with-mouse-events
+    bool m_preventMouseEventForPointerTypeMouse;
+
     // This is set upon sending a pointercancel for touch, prevents PE dispatches for touches until
     // all touch-points become inactive.
     // TODO(mustaq): Consider a state per pointerType, as in PointerIdManager? Exclude mouse?