Revert r158626 "Avoid copying a hash table bucket when inserting..."

The change causes crashes on Linux ASAN bots on
virtual/softwarecompositing/iframes/invisible* tests. Reverting fixed
the failures locally.

BUG=310975
TBR=dglazkov

Review URL: https://codereview.chromium.org/46043011

git-svn-id: svn://svn.chromium.org/blink/trunk@160809 bbb929c8-8fbe-4397-9dbb-9b2b20218538