Update hwui_unit_tests to support running with Vulkan backend.

Added Macros for RENDERTHREAD_TESTS which run these tests using specific backends.
RENDERTHREAD_TESTS - Runs OpenGL, SkiaGL, and SkiaVulkan
RENDERTHREAD_SKIA_TESTS - Runs SkiaGL and SkiaVulkan
RENDERTHREAD_OPENGL_TESTS - Runs OpenGL

Test: manual running of hwui_unit_tests

Change-Id: Ia7420ee7a38803a15e2d58394d14b38cae8208d3
diff --git a/libs/hwui/Properties.cpp b/libs/hwui/Properties.cpp
index 848161e..2c1541d 100644
--- a/libs/hwui/Properties.cpp
+++ b/libs/hwui/Properties.cpp
@@ -222,6 +222,12 @@
     return sRenderPipelineType;
 }
 
+#ifdef HWUI_GLES_WRAP_ENABLED
+void Properties::overrideRenderPipelineType(RenderPipelineType type) {
+    sRenderPipelineType = type;
+}
+#endif
+
 bool Properties::isSkiaEnabled() {
     auto renderType = getRenderPipelineType();
     return RenderPipelineType::SkiaGL == renderType