diff -r 000000000000 -r 6474c204b198 widget/xpwidgets/nsBaseScreen.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/widget/xpwidgets/nsBaseScreen.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,85 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: sw=2 ts=8 et :
+ */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#define MOZ_FATAL_ASSERTIONS_FOR_THREAD_SAFETY
+
+#include "nsBaseScreen.h"
+
+NS_IMPL_ISUPPORTS(nsBaseScreen, nsIScreen)
+
+nsBaseScreen::nsBaseScreen()
+{
+  for (uint32_t i = 0; i < nsIScreen::BRIGHTNESS_LEVELS; i++)
+    mBrightnessLocks[i] = 0;
+}
+
+nsBaseScreen::~nsBaseScreen() { }
+
+NS_IMETHODIMP
+nsBaseScreen::GetRectDisplayPix(int32_t *outLeft,  int32_t *outTop,
+                                int32_t *outWidth, int32_t *outHeight)
+{
+  return GetRect(outLeft, outTop, outWidth, outHeight);
+}
+
+NS_IMETHODIMP
+nsBaseScreen::GetAvailRectDisplayPix(int32_t *outLeft,  int32_t *outTop,
+                                     int32_t *outWidth, int32_t *outHeight)
+{
+  return GetAvailRect(outLeft, outTop, outWidth, outHeight);
+}
+
+NS_IMETHODIMP
+nsBaseScreen::LockMinimumBrightness(uint32_t aBrightness)
+{
+  NS_ABORT_IF_FALSE(
+    aBrightness < nsIScreen::BRIGHTNESS_LEVELS,
+    "Invalid brightness level to lock");
+  mBrightnessLocks[aBrightness]++;
+  NS_ABORT_IF_FALSE(mBrightnessLocks[aBrightness] > 0,
+    "Overflow after locking brightness level");
+
+  CheckMinimumBrightness();
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsBaseScreen::UnlockMinimumBrightness(uint32_t aBrightness)
+{
+  NS_ABORT_IF_FALSE(
+    aBrightness < nsIScreen::BRIGHTNESS_LEVELS,
+    "Invalid brightness level to lock");
+  NS_ABORT_IF_FALSE(mBrightnessLocks[aBrightness] > 0,
+    "Unlocking a brightness level with no corresponding lock");
+  mBrightnessLocks[aBrightness]--;
+
+  CheckMinimumBrightness();
+
+  return NS_OK;
+}
+
+void
+nsBaseScreen::CheckMinimumBrightness()
+{
+  uint32_t brightness = nsIScreen::BRIGHTNESS_LEVELS;
+  for (int32_t i = nsIScreen::BRIGHTNESS_LEVELS - 1; i >=0; i--) {
+    if (mBrightnessLocks[i] > 0) {
+      brightness = i;
+      break;
+    }
+  }
+
+  ApplyMinimumBrightness(brightness);
+}
+
+NS_IMETHODIMP
+nsBaseScreen::GetContentsScaleFactor(double* aContentsScaleFactor)
+{
+  *aContentsScaleFactor = 1.0;
+  return NS_OK;
+}