Call drawPaint instead of drawPath if there's clip (flutter#5937)

If we want to avoid the bleeding edge artifact (flutter#18057 (comment)) using saveLayer, we have to call drawPaint instead of drawPath as anti-aliased drawPath will always have such artifacts.

This is discovered when I try to add golden tests for such bleeding artifacts using our new Clip enum. Here's the updated golden files: flutter/goldens@cb1fa8a?short_path=57b30ce#diff-57b30cea9b10b7ca689009854e12d70e

Author: liyuqian

flow/layers/physical_shape_layer.cc

@@ -87,10 +87,6 @@ void PhysicalShapeLayer::Paint(PaintContext& context) const {
                SkColorGetA(color_) != 0xff, device_pixel_ratio_);
   }
 
-  SkPaint paint;
-  paint.setColor(color_);
-  context.canvas.drawPath(path_, paint);
-
   int saveCount = context.canvas.save();
   switch (clip_behavior_) {
     case Clip::hardEdge:
@@ -107,6 +103,18 @@ void PhysicalShapeLayer::Paint(PaintContext& context) const {
       break;
   }
 
+  SkPaint paint;
+  paint.setColor(color_);
+  if (clip_behavior_ == Clip::none) {
+    context.canvas.drawPath(path_, paint);
+  } else {
+    // If we want to avoid the bleeding edge artifact
+    // (https://github.com/flutter/flutter/issues/18057#issue-328003931)
+    // using saveLayer, we have to call drawPaint instead of drawPath as
+    // anti-aliased drawPath will always have such artifacts.
+    context.canvas.drawPaint(paint);
+  }
+
   PaintChildren(context);
 
   context.canvas.restoreToCount(saveCount);