[ObjC ARC] Converts ios/chrome/browser/ui/colors:colors to ARC.

ios/chrome/browser/ui/colors/MDCPalette+CrAdditions.mm

 // Copyright 2016 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 "ios/chrome/browser/ui/colors/MDCPalette+CrAdditions.h"
 
 #include "ios/web/public/web_thread.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @implementation MDCPalette (CrAdditions)
 
 namespace {
 static MDCPalette* g_bluePalette = nil;
 static MDCPalette* g_redPalette = nil;
 static MDCPalette* g_greenPalette = nil;
 static MDCPalette* g_yellowPalette = nil;
 }
 
 + (MDCPalette*)cr_bluePalette {
@@ skipping 24 matching lines @@
   DCHECK(!web::WebThread::IsThreadInitialized(web::WebThread::UI) ||
          web::WebThread::CurrentlyOn(web::WebThread::UI));
   if (!g_yellowPalette)
     return [MDCPalette yellowPalette];
   return g_yellowPalette;
 }
 
 + (void)cr_setBluePalette:(MDCPalette*)palette {
   DCHECK(!web::WebThread::IsThreadInitialized(web::WebThread::UI) ||
          web::WebThread::CurrentlyOn(web::WebThread::UI));
-  [g_bluePalette autorelease];
-  g_bluePalette = [palette retain];
+  g_bluePalette = palette;
 }
 
 + (void)cr_setRedPalette:(MDCPalette*)palette {
   DCHECK(!web::WebThread::IsThreadInitialized(web::WebThread::UI) ||
          web::WebThread::CurrentlyOn(web::WebThread::UI));
-  [g_redPalette autorelease];
-  g_redPalette = [palette retain];
+  g_redPalette = palette;
 }
 
 + (void)cr_setGreenPalette:(MDCPalette*)palette {
   DCHECK(!web::WebThread::IsThreadInitialized(web::WebThread::UI) ||
          web::WebThread::CurrentlyOn(web::WebThread::UI));
-  [g_greenPalette autorelease];
-  g_greenPalette = [palette retain];
+  g_greenPalette = palette;
 }
 
 + (void)cr_setYellowPalette:(MDCPalette*)palette {
   DCHECK(!web::WebThread::IsThreadInitialized(web::WebThread::UI) ||
          web::WebThread::CurrentlyOn(web::WebThread::UI));
-  [g_yellowPalette autorelease];
-  g_yellowPalette = [palette retain];
+  g_yellowPalette = palette;
 }
 
 @end