Implement GL_OES_EGL_image_external support.

BUG=14610416

Change-Id: I9ca6d1779c7b6f1b28d5d5665264815881ee01b5
Reviewed-on: https://swiftshader-review.googlesource.com/1071
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
diff --git a/src/GLES2/compiler/SymbolTable.cpp b/src/GLES2/compiler/SymbolTable.cpp
index 7113a3a..93937af 100644
--- a/src/GLES2/compiler/SymbolTable.cpp
+++ b/src/GLES2/compiler/SymbolTable.cpp
@@ -52,6 +52,7 @@
     case EbtBool:               mangledName += 'b';      break;
     case EbtSampler2D:          mangledName += "s2";     break;
     case EbtSamplerCube:        mangledName += "sC";     break;
+    case EbtSamplerExternalOES: mangledName += "sE";     break;
     case EbtStruct:
         mangledName += "struct-";
         if (typeName)