Add missing copyright notice to DarkModeFilter files.

Change-Id: Iee9c633bc0b0407cfff511f43735ea5b99e25d41
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1626394
Auto-Submit: Aran Gilman <gilmanmh@google.com>
Commit-Queue: Stephen Chenney <schenney@chromium.org>
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662604}

third_party/blink/renderer/platform/graphics/dark_mode_filter.cc

+// Copyright 2019 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.
+
 #include "third_party/blink/renderer/platform/graphics/dark_mode_filter.h"
 
 #include "base/optional.h"

third_party/blink/renderer/platform/graphics/dark_mode_filter.h

+// Copyright 2019 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.
+
 #ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_GRAPHICS_DARK_MODE_FILTER_H_
 #define THIRD_PARTY_BLINK_RENDERER_PLATFORM_GRAPHICS_DARK_MODE_FILTER_H_