[turbofan] Improve heap broker tracing.

Bug: v8:7790
Change-Id: Ie8b4c84188a123ddec99c65146ddd7c70e1f1b05
Reviewed-on: https://chromium-review.googlesource.com/1236073
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56089}

src/compiler/js-heap-broker.h

@@ -487,6 +487,8 @@ class V8_EXPORT_PRIVATE JSHeapBroker : public NON_EXPORTED_BASE(ZoneObject) {
   ObjectData* GetOrCreateData(Object*);
 
   void Trace(const char* format, ...) const;
+  void IncrementTracingIndentation();
+  void DecrementTracingIndentation();
 
  private:
   friend class HeapObjectRef;
@@ -498,6 +500,8 @@ class V8_EXPORT_PRIVATE JSHeapBroker : public NON_EXPORTED_BASE(ZoneObject) {
   base::Optional<NativeContextRef> native_context_;
   ZoneUnorderedMap<Address, ObjectData*> refs_;
   BrokerMode mode_;
+  unsigned tracing_indentation_ = 0;
+
   static const size_t kInitialRefsBucketCount = 1000;
 };