Parser must be able to operate independent of Isolate and the V8 heap during
parsing. After the heap-independent phase, there is a heap dependent phase,
during which we internalize strings, handle errors, etc.

This makes Isolate (also via CompilationInfo) unaccessible during parsing, and
thus decreases the probability of accidental code changes which would add
heap-dependent operations into the heap-independent phase.

Since Isolate is also accessible via CompilationInfo, now CompilationInfo is
only passed to the entry points of parsing, and not stored in Parser.

R=rossberg@chromium.org
BUG=

Review URL: https://codereview.chromium.org/908173003

Cr-Commit-Position: refs/heads/master@{#26612}