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

src/gpu/vk/GrVkRenderPass.h

Index: src/gpu/vk/GrVkRenderPass.h
diff --git a/src/gpu/vk/GrVkRenderPass.h b/src/gpu/vk/GrVkRenderPass.h
index 2f7e2875427ba05edce0ff6f2bb4b631bd0513e0..1068adaa110491a828f0c93dcadcaa1b8dabd091 100644
--- a/src/gpu/vk/GrVkRenderPass.h
+++ b/src/gpu/vk/GrVkRenderPass.h
@@ -14,6 +14,7 @@
 
 #include "vulkan/vulkan.h"
 
+class GrProcessorKeyBuilder;
 class GrVkGpu;
 class GrVkRenderTarget;
 
@@ -72,6 +73,8 @@ public:
 
     VkRenderPass vkRenderPass() const { return fRenderPass; }
 
+    void genKey(GrProcessorKeyBuilder* b) const;
+
 private:
     GrVkRenderPass(const GrVkRenderPass&);
     GrVkRenderPass& operator=(const GrVkRenderPass&);