Make stylus's eraser button work on Mac

content/browser/renderer_host/render_widget_host_view_mac.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/render_widget_host_view_mac.h"
 
 #import <Carbon/Carbon.h>
 #import <objc/runtime.h>
 #include <OpenGL/gl.h>
 #include <QuartzCore/QuartzCore.h>
@@ skipping 1892 matching lines @@
   TRACE_EVENT0("browser", "RenderWidgetHostViewCocoa::mouseEvent");
   if (responderDelegate_ &&
       [responderDelegate_ respondsToSelector:@selector(handleEvent:)]) {
     BOOL handled = [responderDelegate_ handleEvent:theEvent];
     if (handled)
       return;
   }
 
   // Set the pointer type when we are receiving a NSMouseEntered event and the
   // following NSMouseExited event should have the same pointer type.
+  // For NSMouseExited and NSMouseEntered events, they do not have a subtype.
+  // We decide their pointer types by checking if we recevied a
+  // NSTabletProximity event.
   NSEventType type = [theEvent type];
-  if (type == NSMouseEntered) {
+  if (type == NSMouseEntered || type == NSMouseExited) {
     pointerType_ = isStylusEnteringProximity_
-                       ? blink::WebPointerProperties::PointerType::Pen
+                       ? pointerType_
                        : blink::WebPointerProperties::PointerType::Mouse;
+  } else {
+    NSEventSubtype subtype = [theEvent subtype];
+    // For other mouse events and touchpad events, the pointer type is mouse.
+    if (subtype != NSTabletPointEventSubtype &&
+        subtype != NSTabletProximityEventSubtype) {
+      pointerType_ = blink::WebPointerProperties::PointerType::Mouse;
+    }
   }
 
   if ([self shouldIgnoreMouseEvent:theEvent]) {
     // If this is the first such event, send a mouse exit to the host view.
     if (!mouseEventWasIgnored_ && renderWidgetHostView_->render_widget_host_) {
       WebMouseEvent exitEvent =
           WebMouseEventBuilder::Build(theEvent, self, pointerType_);
       exitEvent.setType(WebInputEvent::MouseLeave);
       exitEvent.button = WebMouseEvent::Button::NoButton;
       renderWidgetHostView_->ForwardMouseEvent(exitEvent);
@@ skipping 52 matching lines @@
   if (renderWidgetHostView_->ShouldRouteEvent(event)) {
     renderWidgetHostView_->render_widget_host_->delegate()
         ->GetInputEventRouter()
         ->RouteMouseEvent(renderWidgetHostView_.get(), &event, latency_info);
   } else {
     renderWidgetHostView_->ProcessMouseEvent(event, latency_info);
   }
 }
 
 - (void)tabletEvent:(NSEvent*)theEvent {
-  if ([theEvent type] == NSTabletProximity)
+  if ([theEvent type] == NSTabletProximity) {
     isStylusEnteringProximity_ = [theEvent isEnteringProximity];
+    NSPointingDeviceType deviceType = [theEvent pointingDeviceType];
+    // For all tablet events, the pointer type will be pen or eraser.
+    pointerType_ = deviceType == NSEraserPointingDevice
+                       ? blink::WebPointerProperties::PointerType::Eraser
+                       : blink::WebPointerProperties::PointerType::Pen;
+  }
 }
 
 - (BOOL)performKeyEquivalent:(NSEvent*)theEvent {
   // |performKeyEquivalent:| is sent to all views of a window, not only down the
   // responder chain (cf. "Handling Key Equivalents" in
   // http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/EventOverview/HandlingKeyEvents/HandlingKeyEvents.html
   // ). We only want to handle key equivalents if we're first responder.
   if ([[self window] firstResponder] != self)
     return NO;
 
@@ skipping 1487 matching lines @@
 
 // "-webkit-app-region: drag | no-drag" is implemented on Mac by excluding
 // regions that are not draggable. (See ControlRegionView in
 // native_app_window_cocoa.mm). This requires the render host view to be
 // draggable by default.
 - (BOOL)mouseDownCanMoveWindow {
   return YES;
 }
 
 @end