Add empty text check for first child of pre in innerHTML.(fixes #1743)
Move Traceable, trace_reflector from utils.rs to trace.rs.(fixes #1748)
auto merge of #1758 : lpy/servo/issue1748, r=Ms2ger

see #1748
Add test
auto merge of #1759 : lpy/servo/issue1743, r=Ms2ger

see #1743
Merge branch 'master' of https://github.com/mozilla/servo into nodelist-1744
#1744 use map, clean up