Temporary check ensuring no regression while we get the wasm code off the GC heap, and
and until we de-contextualize wasm code.

We expect the only embedded objects to be: CEntryStub, undefined, and
the various builtins for throwing exceptions like OOB. These are all immovable
because they are snapshotted. Additionally, we embed references to the FixedArray
that backs WebAssembly.Table. That will be replaced separately with a native data
structure.

Once the Table is native, we can generate Wasm code off the GC heap, as long as the
embedded objects are immutable, which is the property we check for here. 

That greatly simplifies a subsequent step, which is to replace those dependencies 
with a isolate-independent solution. The source of simplification is that we don't 
have to worry about moving pointers.

Bug: 
Change-Id: Id1e41863a2619c2afc50f48416f422012f0c9a24
Reviewed-on: https://chromium-review.googlesource.com/574938Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46749}