Bug: 
Change-Id: I857f8b3f992faf950917060b3fe705bdd45c3ada
Reviewed-on: https://chromium-review.googlesource.com/638339Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47653}

This patch adds a new intrinsic: %DebugTrackRetainingPath(object).
Calling the intrinsic in JS code saves a weak reference to the given
object in GC internal table of tracked objects.

Each subsequent full GC prints to stdout the retaining path for each
tracked object (if it is still alive). The retaining path is the real
path that the marker took from the root set to the tracked object.

This is useful for investigating of memory leaks:
1) Add %DebugTrackRetainingPath(leaking_object) in JS code.
For example:
  function foo() {
    let x = { bar: "bar"};
    %DebugTrackRetainingPath(x);
    return () => { return x; }
  }

  let closure = foo();
  gc();

2) Run d8 with --allow-natives-syntax --track-retaining-path --expose-gc.

3) Check the retaining path in stdout.

For more detailed inspection, run d8 in gdb and set breakpoint in

v8: :internal::Heap::PrintRetainingPath.
Change-Id: I01a0faac1e009bc6c321fa75613900b49d2b036f
Reviewed-on: https://chromium-review.googlesource.com/575972
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46766}

This makes an ObjectVisitor as powerful as a StaticVisitor and allows
slots recording in ObjectVisitor.

This patch also renames VisitCell method of ObjectVisitor to
VisitCellPointer, so that VisitCell is free to be used for actually
visiting a cell.

BUG=chromium:709075

Review-Url: https://codereview.chromium.org/2810653002
Cr-Commit-Position: refs/heads/master@{#44860}

This patch adds a new interface called RootVisitor and changes the root
iteration functions to accept a RootVisitor instead of an ObjectVisitor.

Future CLs will change ObjectVisitor to provide the host object to all
visiting functions, which will bring it in sync with static visitors.

Having separate visitors for roots and objects removes ambiguity in
VisitPointers and reduces chances of forgetting to record slots.

This is intended as pure refactoring. All places that require behavior
change are marked with TODO and will addressed in future CLs.

BUG=chromium:709075

Review-Url: https://codereview.chromium.org/2801073006
Cr-Commit-Position: refs/heads/master@{#44852}