Revert of Rename Heap to ThreadHeap (patchset #13 id:240001 of https://codereview.chromium.org/1845543002/ )

Reason for revert:
Failed memory_test: content_unittests

Original issue's description:
> Rename Heap to ThreadHeap
>
> BUG=591606
> CQ_EXTRA_TRYBOTS=tryserver.chromium.perf:winx64_10_perf_cq;tryserver.chromium.perf:mac_retina_perf_cq;tryserver.chromium.perf:linux_perf_cq
>
> Committed: https://crrev.com/191c640cc25f76c0c0f8a0b448de33cd059f4a8e
> Cr-Commit-Position: refs/heads/master@{#387233}

[email protected],[email protected],[email protected],[email protected]
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=591606

Review URL: https://codereview.chromium.org/1884083002

Cr-Commit-Position: refs/heads/master@{#387254}

Author: keishi

front_end/timeline/TimelineModel.js

@@ -156,7 +156,7 @@ WebInspector.TimelineModel.RecordType = {
     ImplSideFling: "InputHandlerProxy::HandleGestureFling::started",
     GCIdleLazySweep: "ThreadState::performIdleLazySweep",
     GCCompleteSweep: "ThreadState::completeSweep",
-    GCCollectGarbage: "BlinkGCMarking",
+    GCCollectGarbage: "Heap::collectGarbage",
 
     // CpuProfile is a virtual event created on frontend to support
     // serialization of CPU Profiles within tracing timeline data.