Add back door support for GLSL tessellation shaders

Implements tessellation support at the Ganesh level, and adds back
door methods for supplying raw GLSL strings directly to the OpenGL
driver. Adds a new gm to verify tessellation is works in GL.

Change-Id: Idfc285b955cbe5e8e6bf0475be8b518b0cc6ed2c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/261196
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
diff --git a/src/gpu/glsl/GrGLSLGeometryProcessor.cpp b/src/gpu/glsl/GrGLSLGeometryProcessor.cpp
index 6e8b0d7..db28d7b 100644
--- a/src/gpu/glsl/GrGLSLGeometryProcessor.cpp
+++ b/src/gpu/glsl/GrGLSLGeometryProcessor.cpp
@@ -17,6 +17,12 @@
     GrGPArgs gpArgs;
     this->onEmitCode(args, &gpArgs);
 
+    if (args.fGP.willUseTessellationShaders()) {
+        // Tessellation shaders are temporarily responsible for integrating their own code strings
+        // while we work out full support.
+        return;
+    }
+
     GrGLSLVertexBuilder* vBuilder = args.fVertBuilder;
     if (!args.fGP.willUseGeoShader()) {
         // Emit the vertex position to the hardware in the normalized window coordinates it expects.