libgui: Add a test suite for SRGB testing

This is the start of an SRGB test suite. Currently it has a test for
SRGB texture reads in GLES3.

Change-Id: I553ee2691dc92b98cae7a003084d4e2823d40d95
diff --git a/libs/gui/tests/Android.mk b/libs/gui/tests/Android.mk
index db24065..2eeb5c7 100644
--- a/libs/gui/tests/Android.mk
+++ b/libs/gui/tests/Android.mk
@@ -13,6 +13,7 @@
     GLTest.cpp \
     IGraphicBufferProducer_test.cpp \
     MultiTextureConsumer_test.cpp \
+    SRGB_test.cpp \
     SurfaceTextureClient_test.cpp \
     SurfaceTextureFBO_test.cpp \
     SurfaceTextureGLThreadToGL_test.cpp \