Fixes two bugs in tree view: . Invoking SetRootShown before the tree was created resulted in   updating internal structures with wrong info. This caused problems   if you later tried to delete. I've added a DCHECK to make sure we   don't hit this again. . Adding a node to the root when the root wasn't shown silently   failed.
Fixes two bugs in tree view:
. Invoking SetRootShown before the tree was created resulted in
  updating internal structures with wrong info. This caused problems
  if you later tried to delete. I've added a DCHECK to make sure we
  don't hit this again.
. Adding a node to the root when the root wasn't shown silently
  failed.

BUG=none
TEST=make sure bookmark manager doesn't have any problems when
  adding/removing nodes.

Review URL: http://codereview.chromium.org/434053

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@33023 0039d316-1c4b-4281-b951-d872f2087c98

adobe/chromium,Crystalnix/house-of-life-chromium,adobe/chromium,gavinp/chromium,adobe/chromium,ropik/chromium,ropik/chromium,Crystalnix/house-of-life-chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,yitian134/chromium,adobe/chromium,adobe/chromium,ropik/chromium,adobe/chromium,adobe/chromium,Crystalnix/house-of-life-chromium,ropik/chromium,ropik/chromium,Crystalnix/house-of-life-chromium,ropik/chromium,gavinp/chromium,yitian134/chromium,adobe/chromium,yitian134/chromium,ropik/chromium,Crystalnix/house-of-life-chromium,gavinp/chromium,gavinp/chromium,yitian134/chromium,gavinp/chromium,yitian134/chromium,gavinp/chromium,Crystalnix/house-of-life-chromium,gavinp/chromium,yitian134/chromium,yitian134/chromium,ropik/chromium,adobe/chromium,gavinp/chromium,Crystalnix/house-of-life-chromium,adobe/chromium,gavinp/chromium,Crystalnix/house-of-life-chromium,Crystalnix/house-of-life-chromium,adobe/chromium,yitian134/chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,gavinp/chromium,ropik/chromium