Set up cache in vulkan to reuse GrVkPrograms (aka VkPipelines)

src/gpu/GrStencil.h

Index: src/gpu/GrStencil.h
diff --git a/src/gpu/GrStencil.h b/src/gpu/GrStencil.h
index 28042b0b2eb95ef6ad900c1bc0f6c03f3e3aa0a8..fa7d626a8745ed2a0be471da2f585268ae1990eb 100644
--- a/src/gpu/GrStencil.h
+++ b/src/gpu/GrStencil.h
@@ -13,6 +13,8 @@
 #include "GrTypes.h"
 #include "SkRegion.h"
 
+class GrProcessorKeyBuilder;
+
 /**
  * Gr uses the stencil buffer to implement complex clipping inside the
  * GrDrawTarget class. The GrDrawTarget makes a subset of the stencil buffer
@@ -285,6 +287,8 @@ public:
         return fPassOps[0] < kStencilOpCount;
     }
 
+    void genKey(GrProcessorKeyBuilder* b) const;
+
     bool operator == (const GrStencilSettings& s) const {
         static const size_t gCompareSize = sizeof(GrStencilSettings) -
                                            sizeof(fFlags);