SkPDF: SkBitSet gets reset() to make drop() better.

src/pdf/SkPDFFont.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkData.h"
 #include "SkGlyphCache.h"
 #include "SkPaint.h"
@@ skipping 709 matching lines @@
 
 ////////////////////////////////////////////////////////////////////////////////
 
 bool SkPDFFont::CanEmbedTypeface(SkTypeface* typeface, SkPDFCanon* canon) {
     const SkAdvancedTypefaceMetrics* metrics = SkPDFFont::GetMetrics(typeface, canon);
     return metrics && can_embed(*metrics);
 }
 
 void SkPDFFont::drop() {
     fTypeface = nullptr;
+    fGlyphUsage.~SkBitSet();
+    new (&fGlyphUsage) SkBitSet(0);
     this->SkPDFDict::drop();
 }