Implementing gl_InstanceID in the HLSL compiler.

Fixes:
dEQP-GLES3.functional.instanced.draw_arrays_instanced.instance_id
dEQP-GLES3.functional.instanced.draw_arrays_instanced.mixed
dEQP-GLES3.functional.instanced.draw_elements_instanced.instance_id
dEQP-GLES3.functional.instanced.draw_elements_instanced.mixed

BUG=angle:601

Change-Id: I6e120eebc90d00e025fc58f096064e6ed1da826b
Reviewed-on: https://chromium-review.googlesource.com/246911
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Gregoire Payen de La Garanderie <Gregory.Payen@imgtec.com>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
diff --git a/src/compiler/translator/OutputHLSL.h b/src/compiler/translator/OutputHLSL.h
index b6e9db6..dec421c 100644
--- a/src/compiler/translator/OutputHLSL.h
+++ b/src/compiler/translator/OutputHLSL.h
@@ -132,6 +132,7 @@
     bool mUsesPointCoord;
     bool mUsesFrontFacing;
     bool mUsesPointSize;
+    bool mUsesInstanceID;
     bool mUsesFragDepth;
     bool mUsesXor;
     bool mUsesDiscardRewriting;