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/ShaderLang.cpp b/src/compiler/ShaderLang.cpp
index 051e4ec..ab8799c 100644
--- a/src/compiler/ShaderLang.cpp
+++ b/src/compiler/ShaderLang.cpp
@@ -110,12 +110,13 @@
 // Driver calls these to create and destroy compiler objects.
 //
 ShHandle ShConstructCompiler(ShShaderType type, ShShaderSpec spec,
+                             ShShaderOutput output,
                              const ShBuiltInResources* resources)
 {
     if (!InitThread())
         return 0;
 
-    TShHandleBase* base = static_cast<TShHandleBase*>(ConstructCompiler(type, spec));
+    TShHandleBase* base = static_cast<TShHandleBase*>(ConstructCompiler(type, spec, output));
     TCompiler* compiler = base->getAsCompiler();
     if (compiler == 0)
         return 0;