Add "sample locations" feature to GrProcessor

src/gpu/vk/GrVkGpu.h

Index: src/gpu/vk/GrVkGpu.h
diff --git a/src/gpu/vk/GrVkGpu.h b/src/gpu/vk/GrVkGpu.h
index e04095ea71a59a9d896729e6dd4c10b5dcb47d1b..25abace583c2090e83f725b787f4ff414f0700bd 100644
--- a/src/gpu/vk/GrVkGpu.h
+++ b/src/gpu/vk/GrVkGpu.h
@@ -76,6 +76,11 @@ public:
                        const SkIRect& srcRect,
                        const SkIPoint& dstPoint) override;
 
+    void onGetMultisampleSpecs(GrRenderTarget* rt,
+                               const GrStencilSettings&,
+                               int* effectiveSampleCnt,
+                               SkAutoTDeleteArray<SkPoint>*);
+
     bool initCopySurfaceDstDesc(const GrSurface* src, GrSurfaceDesc* desc) const override {
         SkDebugf("initCopySurfaceDstDesc not yet implemented for Vulkan\n");
         return false;