Add buffer helper to read directly into SkString to avoid extra copying

src/core/SkPaintOptionsAndroid.cpp

Index: src/core/SkPaintOptionsAndroid.cpp
diff --git a/src/core/SkPaintOptionsAndroid.cpp b/src/core/SkPaintOptionsAndroid.cpp
index a08845a0b447a8c4a8ecacc45718434095db9df2..46e8060073d3e517662bc530173658cf4f04813d 100644
--- a/src/core/SkPaintOptionsAndroid.cpp
+++ b/src/core/SkPaintOptionsAndroid.cpp
@@ -35,9 +35,9 @@ void SkPaintOptionsAndroid::flatten(SkFlattenableWriteBuffer& buffer) const {
 
 void SkPaintOptionsAndroid::unflatten(SkFlattenableReadBuffer& buffer) {
     fFontVariant = (FontVariant)buffer.readUInt();
-    char* tag = buffer.readString();
+    SkString tag;
+    buffer.readString(&tag);
     fLanguage = SkLanguage(tag);
-    sk_free(tag);
     fUseFontFallbacks = buffer.readBool();
 }