cocoa: darken toolbar buttons in Increase Contrast mode

chrome/browser/ui/cocoa/toolbar/toolbar_button_cocoa.mm

Index: chrome/browser/ui/cocoa/toolbar/toolbar_button_cocoa.mm
diff --git a/chrome/browser/ui/cocoa/toolbar/toolbar_button_cocoa.mm b/chrome/browser/ui/cocoa/toolbar/toolbar_button_cocoa.mm
index 2640313df0a6c88c034a807b846f487b98bbaed1..a363a45e6948dfb917ff55584e66a9d05dbcc71e 100644
--- a/chrome/browser/ui/cocoa/toolbar/toolbar_button_cocoa.mm
+++ b/chrome/browser/ui/cocoa/toolbar/toolbar_button_cocoa.mm
@@ -224,7 +224,11 @@ const NSSize kMDButtonIconSize = NSMakeSize(16, 16);
 }
 
 - (SkColor)vectorIconColor:(BOOL)themeIsDark {
-  return themeIsDark ? SK_ColorWHITE : SkColorSetRGB(0x5A, 0x5A, 0x5A);
+  const ui::ThemeProvider* provider = [[self window] themeProvider];
+  return themeIsDark ? SK_ColorWHITE
+                     : (provider && provider->ShouldIncreaseContrast()
+                            ? SK_ColorBLACK
+                            : SkColorSetRGB(0x5A, 0x5A, 0x5A));
 }
 
 - (NSImage*)browserToolsIconForFillColor:(SkColor)fillColor {