For each Managed<T> (which is a Foreign), we create a weak global handle
with a finalizer which deletes the referenced C++ object once the
Foreign is dead.
Before calling this finalizer, the garbage collector needs to mark the
referenced object black (i.e. live), because the finalizer might
resurrect it.
Since this is never done for managed objects, we can use the more
lightweight phantom handle semantics, which allows the referenced
object to be garbage collected right away.

However, we can't access the global handle via the WeakCallbackInfo,
because the global handle will already be garbage collected. So we need
to store it explicitly. This is solved by storing the global handle
together with the finalizer.
In order to implement this, ownership of the ManagedObjectFinalizer
is moved from the isolate to the managed object.

R=ulan@chromium.org, mtrofin@chromium.org
BUG=v8:6505, chromium:734345

Change-Id: I94a245df601f70e19355d82439d30099e159231b
Reviewed-on: https://chromium-review.googlesource.com/539578
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46036}

Make sure that we call the destructors on all embedded object by
replacing the WasmInterpreterInternals::Delete method by an actual
destructor. This way, the compiler automatically calls destructors on
all embedded objects, in particular the IdentityMap in the CodeMap.

This change also requires to release managed objects *before*
tearing down the heap, because the wasm interpreter, referenced via
Managed<>, contains global handles. When those are destroyed, the
isolate still needs to be intact.

Drive-by: Fix include guard in managed.h.

R=ahaas@chromium.org, ulan@chromium.org, mvstanton@chromium.org
BUG=v8:5822

Change-Id: I9a067f037e013c84e4d697a1e913b27c683bb529
Reviewed-on: https://chromium-review.googlesource.com/466187Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44368}

Native resources allocated by v8, as internal implementation detail,
and held by a Foreign object, must be released when the Isolate is
torn down. Example: wasm::WasmModule allocated by wasm compile, and
held throughout the lifetime of the WebAssembly.Module object.

This change:
- Extends Managed<CppType> with a mechanism for doing just that
- Separates the role of Managed<CppType> to be strictly an owner of
the lifetime of the native resource. For cases where that's not
desirable, we can polymorphically use Foregin.
- moves managed.h out of wasm, since it's not wasm-specific.

BUG=680065

Review-Url: https://codereview.chromium.org/2676513008
Cr-Commit-Position: refs/heads/master@{#43350}