Bug 1259734 - use AppendElements in DisplayItemClip::AppendRoundedRects; r=dholbert

It is shorter and nicer than writing out the loop ourselves.

layout/base/DisplayItemClip.cpp

@@ -403,10 +403,8 @@ DisplayItemClip::GetCommonRoundedRectCount(const DisplayItemClip& aOther,
 void
 DisplayItemClip::AppendRoundedRects(nsTArray<RoundedRect>* aArray, uint32_t aCount) const
 {
-  uint32_t count = std::min(mRoundedClipRects.Length(), size_t(aCount));
-  for (uint32_t i = 0; i < count; ++i) {
-    *aArray->AppendElement() = mRoundedClipRects[i];
-  }
+  size_t count = std::min(mRoundedClipRects.Length(), size_t(aCount));
+  aArray->AppendElements(mRoundedClipRects.Elements(), count);
 }
 
 bool