translator: Fail compilation if precision emu unsupported.

The fuzzer uncovered a case where we were trying to emulate precision
on HLSL 3.0, causing an ASSERT crash.

BUG=chromium:653276

Change-Id: I2e666a1ff4f605541e25f04264146063559cb835
Reviewed-on: https://chromium-review.googlesource.com/394237
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
diff --git a/src/compiler/translator/EmulatePrecision.h b/src/compiler/translator/EmulatePrecision.h
index c2b9857..f23e40b 100644
--- a/src/compiler/translator/EmulatePrecision.h
+++ b/src/compiler/translator/EmulatePrecision.h
@@ -32,6 +32,8 @@
                                const int shaderVersion,
                                const ShShaderOutput outputLanguage);
 
+    static bool SupportedInLanguage(const ShShaderOutput outputLanguage);
+
   private:
     struct TypePair
     {