Fixed compiler warning C4267 'conversion from 'size_t' to 'type', possible loss of data'

BUG=angleproject:1120

Change-Id: I01ef10bea7f487c2b394d030c76628f38d2ea645
Reviewed-on: https://chromium-review.googlesource.com/292780
Tested-by: Cooper Partin <coopp@microsoft.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
diff --git a/src/libANGLE/renderer/d3d/DynamicHLSL.cpp b/src/libANGLE/renderer/d3d/DynamicHLSL.cpp
index 3717f35..7a12d36 100644
--- a/src/libANGLE/renderer/d3d/DynamicHLSL.cpp
+++ b/src/libANGLE/renderer/d3d/DynamicHLSL.cpp
@@ -517,8 +517,9 @@
             // corresponding to unwritten variables are similarly undefined.
             if (outputVariable)
             {
-                declarationHLSL += "    " + HLSLTypeString(outputVariable->type) + " " + outputVariable->name +
-                                   " : " + targetSemantic + Str(layoutIndex) + ";\n";
+                declarationHLSL += "    " + HLSLTypeString(outputVariable->type) + " " +
+                                   outputVariable->name + " : " + targetSemantic +
+                                   Str(static_cast<int>(layoutIndex)) + ";\n";
 
                 copyHLSL += "    output." + outputVariable->name + " = " + outputVariable->source + ";\n";
             }