Adds Scope::MaxNestedContextChainLength() which calculates the maximum length
of the context chain for the given scope. This is used by the interpreter to
preallocate the approprate number of context registers when compiling the
function.

BUG=v8:4280
LOG=N

Review URL: https://codereview.chromium.org/1404793004

Cr-Commit-Position: refs/heads/master@{#31309}