Fix float-int conversion return type precision tracking

Float-int conversion functions are defined to always return highp values.

BUG=angleproject:865
TEST=angle_unittests

Change-Id: Idf243b483f7b5edfcb54de2755af11e17c3756d3
Reviewed-on: https://chromium-review.googlesource.com/262413
Tested-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Nicolas Capens <capn@chromium.org>
diff --git a/src/compiler/translator/Intermediate.cpp b/src/compiler/translator/Intermediate.cpp
index 5e0edfd..fd0038d 100644
--- a/src/compiler/translator/Intermediate.cpp
+++ b/src/compiler/translator/Intermediate.cpp
@@ -189,6 +189,10 @@
 
     switch (op)
     {
+      case EOpFloatBitsToInt:
+      case EOpFloatBitsToUint:
+      case EOpIntBitsToFloat:
+      case EOpUintBitsToFloat:
       case EOpPackSnorm2x16:
       case EOpPackUnorm2x16:
       case EOpPackHalf2x16: