Implement ES2 backend for Angle translator.

With this CL, we have the option to select a code output backend: GLSL, GLSL ES, or HLSL.

Note that we always emit the highest supported float precision for fragment shader due to anglebug 168.  Although this is a temporary solution, it's not against GLSL ES spec, because it's ok for implementation to upgrade precision.

Tested with WebGL conformance test suite, GLES2 conformance test suite (only failed 2/1198), and a few webgl demos, including worlds of webgl, aquarium, etc.

anglebug=81
test=translator emitting correct GLSL ES code when ES2 backend is selected.
Review URL: http://codereview.appspot.com/4550129

git-svn-id: https://angleproject.googlecode.com/svn/trunk@687 736b8ea6-26fd-11df-bfd4-992fa37f6226
diff --git a/src/compiler/CodeGenHLSL.cpp b/src/compiler/CodeGenHLSL.cpp
index e04e789..f46ff66 100644
--- a/src/compiler/CodeGenHLSL.cpp
+++ b/src/compiler/CodeGenHLSL.cpp
@@ -11,9 +11,15 @@
 // compile object used by higher level code.  It returns
 // a subclass of TCompiler.
 //
-TCompiler* ConstructCompiler(ShShaderType type, ShShaderSpec spec)
+TCompiler* ConstructCompiler(
+    ShShaderType type, ShShaderSpec spec, ShShaderOutput output)
 {
-    return new TranslatorHLSL(type, spec);
+  switch (output) {
+    case SH_HLSL_OUTPUT:
+      return new TranslatorHLSL(type, spec);
+    default:
+      return NULL;
+  }
 }
 
 //