If the shared function info is newly compiled when looking for
it in the script (Debug::FindSharedFunctionInfoInScript), then
we can bypass iterating the heap to find JSFunctions referencing
it (Debug::PrepareFunctionForBreakpoints).

BUG=v8:4553
LOG=N

Review URL: https://codereview.chromium.org/1454673002

Cr-Commit-Position: refs/heads/master@{#32107}