Fix truncation of sigma parameter in blur-mask-filtered mask key

This would allow blur-masks alias one another.

Bug: 912595
Bug: 878195
Change-Id: I44e86e893a505cf8abd991975a025cda52011db6
Reviewed-on: https://skia-review.googlesource.com/c/181902
Commit-Queue: Robert Phillips <[email protected]>
Reviewed-by: Florin Malita <[email protected]>

Author: rphilli

src/gpu/GrBlurUtils.cpp

@@ -371,7 +371,7 @@ static void draw_shape_with_mask_filter(GrContext* context,
         SkAssertResult(as_MFB(maskFilter)->asABlur(&rec));
 
         builder[5] = rec.fStyle;  // TODO: we could put this with the other style bits
-        builder[6] = rec.fSigma;
+        builder[6] = SkFloat2Bits(rec.fSigma);
         shape->writeUnstyledKey(&builder[7]);
     }