[Mac] Use a nonactivating panel for notifications so that mouse down doesn't activate Chrome.

ui/message_center/cocoa/popup_controller.mm

 // Copyright (c) 2013 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.
 
 #import "ui/message_center/cocoa/popup_controller.h"
 
 #include <cmath>
 
 #import "base/mac/foundation_util.h"
 #import "base/mac/sdk_forward_declarations.h"
@@ skipping 13 matching lines @@
 // |boundsAnimation_|.
 - (void)setBoundsAnimation:(NSViewAnimation*)animation;
 
 // Constructs an NSViewAnimation from |dictionary|, which should be a view
 // animation dictionary.
 - (NSViewAnimation*)animationWithDictionary:(NSDictionary*)dictionary;
 @end
 
 // Window Subclass /////////////////////////////////////////////////////////////
 
-@interface MCPopupWindow : NSWindow {
+@interface MCPopupWindow : NSPanel {
   // The cumulative X and Y scrollingDeltas since the -scrollWheel: event began.
   NSPoint totalScrollDelta_;
 }
 @end
 
 @implementation MCPopupWindow
 
 - (void)scrollWheel:(NSEvent*)event {
   // Gesture swiping only exists on 10.7+.
   if (![event respondsToSelector:@selector(phase)])
@@ skipping 46 matching lines @@
 
 @end
 
 ////////////////////////////////////////////////////////////////////////////////
 
 @implementation MCPopupController
 
 - (id)initWithNotification:(const message_center::Notification*)notification
              messageCenter:(message_center::MessageCenter*)messageCenter
            popupCollection:(MCPopupCollection*)popupCollection {
-  base::scoped_nsobject<MCPopupWindow> window(
-      [[MCPopupWindow alloc] initWithContentRect:ui::kWindowSizeDeterminedLater
-                                       styleMask:NSBorderlessWindowMask
-                                         backing:NSBackingStoreBuffered
-                                           defer:NO]);
+  base::scoped_nsobject<MCPopupWindow> window([[MCPopupWindow alloc]
+      initWithContentRect:ui::kWindowSizeDeterminedLater
+                styleMask:NSNonactivatingPanelMask
+                  backing:NSBackingStoreBuffered
+                    defer:NO]);
   if ((self = [super initWithWindow:window])) {
     messageCenter_ = messageCenter;
     popupCollection_ = popupCollection;
     notificationController_.reset(
         [[MCNotificationController alloc] initWithNotification:notification
                                                  messageCenter:messageCenter_]);
-    isClosing_ = NO;
     bounds_ = [[notificationController_ view] frame];
 
-    [window setReleasedWhenClosed:NO];
-
-    [window setLevel:NSFloatingWindowLevel];
-    [window setExcludedFromWindowsMenu:YES];
+    [window setFloatingPanel:YES];
+    [window setBecomesKeyOnlyIfNeeded:YES];

[tapted, 2016/10/11 03:55:44]

ah-ha! So If I comment out this line, then crbug.com/459306 easily reproduces
for me again with this patched in (maybe worth trying out so you have an idea of
the badness).

So perhaps so long as we don't put textfields into the notification I think this
will hold up -- we're essentially just adding an alternative workaround. I'm
pretty sure we don't put textfields in - but we _do_ have buttons. However, said
buttons are not keyboard accessible. But if we want them to be, then this bug
might crop up again. (and it's possible a way to resolve the issue then is to
have canBecomeKeyWindow report YES rather than NO). But, maybe we'll have native
notifications by then.

The CL description still needs to be updated - please remove any mention of
apps.

I also wouldn't use a tricky repro as a justification for risk taking. However,
since we've narrowed it down to this `setBecomesKeyOnlyIfNeeded` line, then we
should talk about that instead.

     [window
         setCollectionBehavior:NSWindowCollectionBehaviorCanJoinAllSpaces |
-                              NSWindowCollectionBehaviorIgnoresCycle |
                               NSWindowCollectionBehaviorFullScreenAuxiliary];
 
     [window setHasShadow:YES];
     [window setContentView:[notificationController_ view]];
 
     trackingArea_.reset(
         [[CrTrackingArea alloc] initWithRect:NSZeroRect
                                      options:NSTrackingInVisibleRect |
                                              NSTrackingMouseEnteredAndExited |
                                              NSTrackingActiveAlways
@@ skipping 159 matching lines @@
 
 - (void)mouseEntered:(NSEvent*)event {
   messageCenter_->PausePopupTimers();
 }
 
 - (void)mouseExited:(NSEvent*)event {
   messageCenter_->RestartPopupTimers();
 }
 
 @end