Simplify timeline backend

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index 9186ce6af3d28f43941a7b1af74a64e9fa81e7f1..6b0186cf0c24ef8a1a41684f7063dca00778deda 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -5887,8 +5887,7 @@ DART_EXPORT bool Dart_TimelineGetTrace(Dart_StreamConsumer consumer,
   }
   Thread* T = Thread::Current();
   StackZone zone(T);
-  // Reclaim all blocks cached by isolate.
-  Timeline::ReclaimIsolateBlocks();
+  Timeline::ReclaimCachedBlocksFromThreads();
   JSONStream js;
   IsolateTimelineEventFilter filter(isolate);
   timeline_recorder->PrintTraceEvent(&js, &filter);
@@ -5912,8 +5911,7 @@ DART_EXPORT bool Dart_GlobalTimelineGetTrace(Dart_StreamConsumer consumer,
   }
   Thread* T = Thread::Current();
   StackZone zone(T);
-  // Reclaim all blocks cached in the system.
-  Timeline::ReclaimAllBlocks();
+  Timeline::ReclaimCachedBlocksFromThreads();
   JSONStream js;
   TimelineEventFilter filter;
   timeline_recorder->PrintTraceEvent(&js, &filter);