[heap] Always use the passed-in collector in CollectGarbage.

Do not overwrite a collector decision.

BUG=

Review-Url: https://codereview.chromium.org/2336943003
Cr-Commit-Position: refs/heads/master@{#39585}

src/heap/heap.cc

@@ -972,22 +972,6 @@ bool Heap::CollectGarbage(GarbageCollector collector,
     }
   }
 
-  if (collector == MARK_COMPACTOR && !ShouldFinalizeIncrementalMarking() &&
-      !ShouldAbortIncrementalMarking() && !incremental_marking()->IsStopped() &&
-      !incremental_marking()->should_hurry() && FLAG_incremental_marking &&
-      OldGenerationAllocationLimitReached()) {
-    if (!incremental_marking()->IsComplete() &&
-        !mark_compact_collector()->marking_deque_.IsEmpty() &&
-        !FLAG_gc_global) {
-      if (FLAG_trace_incremental_marking) {
-        isolate()->PrintWithTimestamp(
-            "[IncrementalMarking] Delaying MarkSweep.\n");
-      }
-      collector = SCAVENGER;
-      collector_reason = "incremental marking delaying mark-sweep";
-    }
-  }
-
   bool next_gc_likely_to_collect_more = false;
   intptr_t committed_memory_before = 0;