This also refactors the way we set the length of an arrays' backing
store to use the new elements accessor interface. The actual fix is in
DictionaryElementsAccessor::SetLengthWithoutNormalize() where we first
search for non-deletable elements according to ES5 section 15.4.5.2
specifications.

Snippet from the specification: Attempting to set the length property of
an Array object to a value that is numerically less than or equal to the
largest numeric property name of an existing array indexed non-deletable
property of the array will result in the length being set to a numeric
value that is one greater than that largest numeric property name.

R=danno@chromium.org
TEST=test262/15.4.4.??-7-b-16

Review URL: http://codereview.chromium.org/8372064

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9911 ce2b1a6d-e550-0410-aec6-3dcde31c8c00