[heap] Remove outdated description of marking

Bug: 
Change-Id: Ifc7e6dd429b18793fc6f91ce5f01a534d8437df6
Reviewed-on: https://chromium-review.googlesource.com/711853Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48447}

src/heap/mark-compact.cc

@@ -1077,35 +1077,6 @@ void MarkCompactCollector::Finish() {
   heap_->incremental_marking()->ClearIdleMarkingDelayCounter();
 }
 
-
-// -------------------------------------------------------------------------
-// Phase 1: tracing and marking live objects.
-//   before: all objects are in normal state.
-//   after: a live object's map pointer is marked as '00'.
-
-// Marking all live objects in the heap as part of mark-sweep or mark-compact
-// collection.  Before marking, all objects are in their normal state.  After
-// marking, live objects' map pointers are marked indicating that the object
-// has been found reachable.
-//
-// The marking algorithm is a (mostly) depth-first (because of possible stack
-// overflow) traversal of the graph of objects reachable from the roots.  It
-// uses an explicit stack of pointers rather than recursion.  The young
-// generation's inactive ('from') space is used as a marking stack.  The
-// objects in the marking stack are the ones that have been reached and marked
-// but their children have not yet been visited.
-//
-// The marking stack can overflow during traversal.  In that case, we set an
-// overflow flag.  When the overflow flag is set, we continue marking objects
-// reachable from the objects on the marking stack, but no longer push them on
-// the marking stack.  Instead, we mark them as both marked and overflowed.
-// When the stack is in the overflowed state, objects marked as overflowed
-// have been reached and marked but their children have not been visited yet.
-// After emptying the marking stack, we clear the overflow flag and traverse
-// the heap looking for objects marked as overflowed, push them on the stack,
-// and continue with marking.  This process repeats until all reachable
-// objects have been marked.
-
 class MarkCompactMarkingVisitor final
     : public MarkingVisitor<MarkCompactMarkingVisitor> {
  public: