Implement path cover with nv_path_rendering

src/gpu/gl/GrGpuGL_program.cpp

Index: src/gpu/gl/GrGpuGL_program.cpp
diff --git a/src/gpu/gl/GrGpuGL_program.cpp b/src/gpu/gl/GrGpuGL_program.cpp
index 92eed8d9bb85751e6736408d3ec881e69a21f114..f3b566c20934b7d85019836ed61ef8b8f4454fc1 100644
--- a/src/gpu/gl/GrGpuGL_program.cpp
+++ b/src/gpu/gl/GrGpuGL_program.cpp
@@ -252,6 +252,9 @@ bool GrGpuGL::flushGraphicsState(DrawType type, const GrDeviceCoordTexture* dstC
             SkDEBUGFAIL("Failed to create program!");
             return false;
         }
+
+        SkASSERT(kFillPath_DrawType != type || !fCurrentProgram->hasVertexShader());
+
         fCurrentProgram.get()->ref();
 
         GrGLuint programID = fCurrentProgram->programID();