Auto-dark mode prototype

Experimental force_dark prototype mode. Enabled
by setting debug.hwui.force_dark to true.

Test: verified nothing changes without prop being set

Change-Id: Ib02f3f1a9c591cab1f312b827451f04c782c2f41
diff --git a/libs/hwui/CanvasTransform.h b/libs/hwui/CanvasTransform.h
new file mode 100644
index 0000000..f71fdfa
--- /dev/null
+++ b/libs/hwui/CanvasTransform.h
@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <SkCanvas.h>
+#include <SkPaintFilterCanvas.h>
+
+#include <memory>
+
+namespace android::uirenderer {
+
+enum class UsageHint {
+    Unknown = 0,
+    Background = 1,
+};
+
+enum class ColorTransform {
+    None,
+    Light,
+    Dark,
+};
+
+std::unique_ptr<SkCanvas> makeTransformCanvas(SkCanvas* inCanvas, ColorTransform transform);
+std::unique_ptr<SkCanvas> makeTransformCanvas(SkCanvas* inCanvas, UsageHint usageHint);
+
+}  // namespace android::uirenderer;
\ No newline at end of file