Move WidgetHierarchyUpdatesSuspensionScope into removeChildren loop

NOTE: This is Obsolete. We need to find a better way to write that whole loop. I rolled out my original patch until then.

Move WidgetHierarchyUpdatesSuspensionScope into removeChildren loop

r148127 seems to be causing tons of crashes on myspace.com and others
when doing Widget heirachy updates. It's not clear why this happens
since you need to use the back button to cause it, but moving the
WidgetHierarchyUpdatesSuspensionScope into the loop fixes it. This
makes sense since we shouldn't let script run while the Widget tree
is in an invalid state.

I don't know how to write a LayoutTest for this change.

R=eseidel@chromium.org
CC=karen@chromium.org,jamesr@chromium.org
BUG=230592