Add support for a new GPU interface

include/gpu/GrTypes.h

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrTypes_DEFINED
 #define GrTypes_DEFINED
 
@@ skipping 108 matching lines @@
     return n ? (1 << (32 - SkCLZ(n - 1))) : 1;
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 /**
  * Possible 3D APIs that may be used by Ganesh.
  */
 enum GrBackend {
     kOpenGL_GrBackend,
+    kVulkan_GrBackend,
+
+    kLast_GrBackend = kVulkan_GrBackend
 };
+const int kBackendCount = kLast_GrBackend + 1;
 
 /**
  * Backend-specific 3D context handle
  *      GrGLInterface* for OpenGL. If NULL will use the default GL interface.
  */
 typedef intptr_t GrBackendContext;
 
 ///////////////////////////////////////////////////////////////////////////////
 
 /**
@@ skipping 479 matching lines @@
             return 4 * width * height;
     }
 }
 
 /**
  * This value translates to reseting all the context state for any backend.
  */
 static const uint32_t kAll_GrBackendState = 0xffffffff;
 
 #endif