Merge to XFA: Tidy up JS_Object.h and JS_Object.cpp. (cherry picked from commit b0b1a8bd45ed72e4fd22f5f0a394b7897ae573c7) Original Review URL: https://codereview.chromium.org/1293673003 . TBR=thestig@chromium.org Review URL: https://codereview.chromium.org/1292283002 .