ES31: Implement GL_OES_geometry_shader built-ins in GLSL compiler

This patch intends to implement all built-in constants, variables and
functions defined in OpenGL ES 3.1 extension GL_OES_geometry_shader
in ANGLE GLSL compiler.

1. Add all built-in constants defined in GL_OES_geometry_shader.
2. Add built-in functions EmitVertex() and EndPrimitive() required
   in Geometry Shader.
3. Add built-in variables gl_PrimitiveIDIn and gl_InvocationID to
   Geometry Shader.
4. Add built-in variables gl_PrimitiveID and gl_Layer to both
   Geometry Shader and Fragment Shader when GL_OES_geometry_shader
   is enabled.

BUG=angleproject:1941
TEST=angle_unittests

Change-Id: I92821553ed0efee2ccb77fead6e065e7799819d0
Reviewed-on: https://chromium-review.googlesource.com/627670
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/compiler/translator/SymbolTable.cpp b/src/compiler/translator/SymbolTable.cpp
index 5d15c9b..1c2de5c 100644
--- a/src/compiler/translator/SymbolTable.cpp
+++ b/src/compiler/translator/SymbolTable.cpp
@@ -557,6 +557,16 @@
     insert(level, new TFunction(this, NewPoolTString(name), rvalue, op));
 }
 
+void TSymbolTable::insertBuiltInFunctionNoParametersExt(ESymbolLevel level,
+                                                        const char *ext,
+                                                        TOperator op,
+                                                        const TType *rvalue,
+                                                        const char *name)
+{
+    insertUnmangledBuiltInName(name, level);
+    insert(level, new TFunction(this, NewPoolTString(name), rvalue, op, ext));
+}
+
 TPrecision TSymbolTable::getDefaultPrecision(TBasicType type) const
 {
     if (!SupportsPrecision(type))