DevTools: Don't take into account phantom edges when calculating distances

Do not take into account the following edges when calculating distances:
  - sloppy_function_map in NativeContext
  - descriptors outgoing DescriptorArray

BUG=413608

Review URL: https://codereview.chromium.org/569273002

git-svn-id: svn://svn.chromium.org/blink/trunk@182232 bbb929c8-8fbe-4397-9dbb-9b2b20218538