[Mac][Material Design] Adjust cutoff for detecting a "dark" theme.

chrome/browser/ui/cocoa/chrome_browser_window.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.
 
 #import "chrome/browser/ui/cocoa/chrome_browser_window.h"
 
 #include "base/logging.h"
 #include "chrome/browser/themes/theme_properties.h"
 #import "chrome/browser/ui/cocoa/themed_window.h"
 #include "ui/base/theme_provider.h"
 
+namespace {
+
+// Upper and lower bounds for determining if a theme's colors indicate that
+// it's a "dark" theme. In Material Design, dark themes have controls that are
+// drawn using transparent white instead of a transparent shade of gray.
+const CGFloat kDarkThemeToolbarColorUpperBound = 0.55;
+const CGFloat kDarkThemeTabTextColorLowerBound = 0.7;
+
+}  // namespace
+
 @interface NSWindow (Private)
 - (BOOL)hasKeyAppearance;
 @end
 
 @implementation ChromeBrowserWindow
 
 - (const ui::ThemeProvider*)themeProvider {
   id delegate = [self delegate];
   if (![delegate respondsToSelector:@selector(themeProvider)])
     return NULL;
@@ skipping 36 matching lines @@
 
   // If the custom theme has a custom toolbar color, return YES if it's
   // dark.
   if (themeProvider->HasCustomColor(ThemeProperties::COLOR_TOOLBAR)) {
     NSColor* theColor =
         themeProvider->GetNSColor(ThemeProperties::COLOR_TOOLBAR);
     theColor =
         [theColor colorUsingColorSpaceName:NSCalibratedWhiteColorSpace];
     if (theColor != nil) {
       // The white componement cutoff is an empirical value.
-      return [theColor whiteComponent] < 0.7;
+      return [theColor whiteComponent] < kDarkThemeToolbarColorUpperBound;
     }
   }
 
   // If the custom theme has a custom tab text color, assume that a light
   // color means a dark tab background image, and therefore a dark theme.
   if (themeProvider->HasCustomColor(ThemeProperties::COLOR_TAB_TEXT)) {
     NSColor* theColor =
         themeProvider->GetNSColor(ThemeProperties::COLOR_TAB_TEXT);
     theColor =
         [theColor colorUsingColorSpaceName:NSCalibratedWhiteColorSpace];
     if (theColor != nil) {
-      return [theColor whiteComponent] >= 0.7;
+      return [theColor whiteComponent] >= kDarkThemeTabTextColorLowerBound;
     }
   }
 
   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