[interpreter] A couple of minor tweaks to BytecodeArray.

[interpreter] A couple of minor tweaks to BytecodeArray.

 - Ensure frame_size is always set during allocation.
 - Add DCHECKs that frame_size is a valid value
 - Remove locals_count, which we don't need yet (possibly every)
 - Add a newline at the end of BytecodeArray::Dissassemble
   for each bytecode.

BUG=v8:4280
LOG=N

Review URL: https://codereview.chromium.org/1254873002

Cr-Commit-Position: refs/heads/master@{#29852}