Bookmarks: Fix a script error when deleting multiple folders.
Bookmarks: Fix a script error when deleting multiple folders.

When deleting multiple folders we get callback after each remove and this can trigger a selection change which in turn triggers a call to getSubtree for a folder that was just removed. When this happens we finish the Promise with the value undefined.

BUG=None
TEST=Create two folders and select both. Hit Delete and check that we do not get a script error. (We still get an error from the extension API that the id no longer exists but at least we do not keel over.

Review URL: http://codereview.chromium.org/2647001

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@48938 0039d316-1c4b-4281-b951-d872f2087c98

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