Fix caching of sample locations

include/gpu/GrRenderTarget.h

Index: include/gpu/GrRenderTarget.h
diff --git a/include/gpu/GrRenderTarget.h b/include/gpu/GrRenderTarget.h
index ff75af37e8fe49426db0365b3532a25872446b9a..77b04d24d3f993d1cafbf30712ca34afe79b1f3c 100644
--- a/include/gpu/GrRenderTarget.h
+++ b/include/gpu/GrRenderTarget.h
@@ -163,6 +163,7 @@ protected:
                    SampleConfig sampleConfig, GrStencilAttachment* stencil = nullptr)
         : INHERITED(gpu, desc)
         , fStencilAttachment(stencil)
+        , fMultisampleSpecsID(0)
         , fSampleConfig(sampleConfig)
         , fLastDrawTarget(nullptr) {
         fResolveRect.setLargestInverted();
@@ -184,6 +185,7 @@ private:
     friend class GrRenderTargetPriv;
 
     GrStencilAttachment*  fStencilAttachment;
+    uint8_t               fMultisampleSpecsID;
     SampleConfig          fSampleConfig;
 
     SkIRect               fResolveRect;