This will disable the behavior on Windows 10 in which

ui/views/win/hwnd_message_handler.cc

 // 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 "ui/views/win/hwnd_message_handler.h"
 
 #include <dwmapi.h>
 #include <oleacc.h>
 #include <shellapi.h>
 #include <tchar.h>
@@ skipping 1546 matching lines @@
   SetMsgHandled(FALSE);
   return MA_ACTIVATE;
 }
 
 LRESULT HWNDMessageHandler::OnMouseRange(UINT message,
                                          WPARAM w_param,
                                          LPARAM l_param) {
   return HandleMouseEventInternal(message, w_param, l_param, true);
 }
 
+// On some systems with a high-resolution track pad and running Windows 10,
+// using the scrolling gesture (two-finger scroll) on the track pad
+// causes it to also generate a WM_POINTERDOWN message if the window
+// isn't focused. This leads to a WM_POINTERACTIVATE message and the window
+// gaining focus and coming to the front. This code detects a
+// WM_POINTERACTIVATE coming from the track pad and kills the activation
+// of the window. NOTE: most other trackpad messages come in as mouse
+// messages, including WM_MOUSEWHEEL instead of WM_POINTERWHEEL.
+LRESULT HWNDMessageHandler::OnPointerActivate(UINT message,
+                                              WPARAM w_param,
+                                              LPARAM l_param) {
+  typedef BOOL(WINAPI *GetPointerTypeFn)(UINT32, POINTER_INPUT_TYPE *);

[sky, 2016/04/12 13:19:16]

using?

[kylix_rd, 2016/04/12 14:32:27]

Had to look that up... not quite fully up-to-speed on newer C++11 syntax.
"using" is a way nicer syntax for function pointer decls.

+  UINT32 pointerId = GET_POINTERID_WPARAM(w_param);

[sky, 2016/04/12 13:19:16]

pointer_id

[kylix_rd, 2016/04/12 14:32:28]

Done.

+  POINTER_INPUT_TYPE pointerType;

[sky, 2016/04/12 13:19:16]

pointer_type

[kylix_rd, 2016/04/12 14:32:28]

Done.

+  static GetPointerTypeFn get_pointer_type = reinterpret_cast<GetPointerTypeFn>(
+    GetProcAddress(GetModuleHandleA("user32.dll"), "GetPointerType"));

[sky, 2016/04/12 13:19:16]

make sure you run git cl format (I think this should be a 4 line indent, but I
could be wrong).

[kylix_rd, 2016/04/12 14:32:28]

Done.

+  if (get_pointer_type && get_pointer_type(pointerId, &pointerType)) {
+    if (pointerType == PT_TOUCHPAD) {

[sky, 2016/04/12 13:19:16]

Combine these into a single if statement.

[kylix_rd, 2016/04/12 14:32:27]

Done.

+      return PA_NOACTIVATE;
+    }
+  }
+  SetMsgHandled(FALSE);
+  return -1;
+}
+
 void HWNDMessageHandler::OnMove(const gfx::Point& point) {
   delegate_->HandleMove();
   SetMsgHandled(FALSE);
 }
 
 void HWNDMessageHandler::OnMoving(UINT param, const RECT* new_bounds) {
   delegate_->HandleMove();
 }
 
 LRESULT HWNDMessageHandler::OnNCActivate(UINT message,
@@ skipping 1052 matching lines @@
     delegate_->HandleClientSizeChanged(GetClientAreaBounds().size());
     ResetWindowRegion(false, true);
   }
 
   if (direct_manipulation_helper_)
     direct_manipulation_helper_->SetBounds(bounds_in_pixels);
 }
 
 
 }  // namespace views