Implement trunc, round, roundEven (Emulated roundEven)

BUG=angle:934

Change-Id: If33256bf3707f3f0202147276c71f08c65518205
Reviewed-on: https://chromium-review.googlesource.com/254842
Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>
diff --git a/src/compiler/translator/OutputGLSLBase.cpp b/src/compiler/translator/OutputGLSLBase.cpp
index cea2b4a..4827ee1 100644
--- a/src/compiler/translator/OutputGLSLBase.cpp
+++ b/src/compiler/translator/OutputGLSLBase.cpp
@@ -549,6 +549,15 @@
       case EOpFloor:
         preString = "floor(";
         break;
+      case EOpTrunc:
+        preString = "trunc(";
+        break;
+      case EOpRound:
+        preString = "round(";
+        break;
+      case EOpRoundEven:
+        preString = "roundEven(";
+        break;
       case EOpCeil:
         preString = "ceil(";
         break;