Fix mixed samples stencil clip

src/gpu/GrClipMaskManager.cpp

Index: src/gpu/GrClipMaskManager.cpp
diff --git a/src/gpu/GrClipMaskManager.cpp b/src/gpu/GrClipMaskManager.cpp
index 076871ca05b25a001f66ef790de30c87d1d7dfd9..d5da16b256b7e297efa0e1ba4db7fbbeec8c756e 100644
--- a/src/gpu/GrClipMaskManager.cpp
+++ b/src/gpu/GrClipMaskManager.cpp
@@ -368,8 +368,23 @@ bool GrClipMaskManager::setupClipping(const GrPipelineBuilder& pipelineBuilder,
         }
     }
 
-    // If MSAA is enabled we can do everything in the stencil buffer.
-    if (0 == rt->numStencilSamples() && requiresAA) {
+    SkASSERT(!pipelineBuilder.isHWAntialias() || rt->isStencilBufferMultisampled());
+
+    bool hasHWAntialias = pipelineBuilder.isHWAntialias();
+
+    if (rt->isStencilBufferMultisampled() && !hasHWAntialias) {
+        if (!this->caps()->multisampleDisableSupport()) {
+            hasHWAntialias = true; // This will be on regardless, it's impossible to turn it off.
+        } else if (this->caps()->programmableSampleLocationsSupport()) {
+            // Enable HW antialias, but leave the draw non-antialiased by co-centering the samples.
+            out->fAdditionalPipelineFlags |= GrPipeline::kHWAA_Flag |
+                                             GrPipeline::kCoCenterSamples_Flag;
+            hasHWAntialias = true;
+        }
+    }
+
+    // If we have HW antialias, or don't need AA, we can do everything in the stencil buffer.
+    if (!hasHWAntialias && requiresAA) {
         SkAutoTUnref<GrTexture> result;
 
         // The top-left of the mask corresponds to the top-left corner of the bounds.