Mac: Use a "less" private API for keeping traffic lights lit while bubbles are showing

chrome/browser/ui/cocoa/chrome_browser_window.mm

Index: chrome/browser/ui/cocoa/chrome_browser_window.mm
diff --git a/chrome/browser/ui/cocoa/chrome_browser_window.mm b/chrome/browser/ui/cocoa/chrome_browser_window.mm
index 4f12cda64c98aba999a2426561aefb03589afbcf..e9894b36ce691eeb6445bb8c4415253452c16b99 100644
--- a/chrome/browser/ui/cocoa/chrome_browser_window.mm
+++ b/chrome/browser/ui/cocoa/chrome_browser_window.mm
@@ -9,6 +9,10 @@
 #import "chrome/browser/ui/cocoa/themed_window.h"
 #include "ui/base/theme_provider.h"
 
+@interface NSWindow (Private)
+- (BOOL)hasKeyAppearance;
+@end
+
 @implementation ChromeBrowserWindow
 
 - (const ui::ThemeProvider*)themeProvider {
@@ -80,4 +84,22 @@
   return NO;
 }
 
+- (BOOL)hasKeyAppearance {
+  // If not key, but a non-main child window without its own traffic lights _is_
+  // key, then show this window with key appearance to keep the traffic lights
+  // lit. This does not currently handle WebModal dialogs, since they are
+  // children of an overlay window. But WebModals also temporarily lose key
+  // status while animating closed, so extra logic is needed to avoid flicker.
+  // Start with an early exit, since this is called for every mouseMove and
+  // every cursor blink in an NSTextField.
+  if (![self isKeyWindow]) {
+    for (NSWindow* child in [self childWindows]) {
+      if ([child isKeyWindow] && ![child isMainWindow] &&
+          ([child styleMask] & NSClosableWindowMask) == 0)
+        return YES;
+    }
+  }
+  return [super hasKeyAppearance];
+}
+
 @end