[vm] Fix flaky crash in StackTraceMallocHookLengthTest.

runtime/vm/malloc_hooks_test.cc

Index: runtime/vm/malloc_hooks_test.cc
diff --git a/runtime/vm/malloc_hooks_test.cc b/runtime/vm/malloc_hooks_test.cc
index b9bb73e8c89ca262731d85521d1a3b9bac5ac733..aa4c5374f04253fb85b413832ecc9a9ec31f14b8 100644
--- a/runtime/vm/malloc_hooks_test.cc
+++ b/runtime/vm/malloc_hooks_test.cc
@@ -30,7 +30,6 @@ class EnableMallocHooksScope : public ValueObject {
   EnableMallocHooksScope() {
     saved_enable_malloc_hooks_ = FLAG_profiler_native_memory;
     FLAG_profiler_native_memory = true;
-    Profiler::InitAllocationSampleBuffer();
     MallocHooks::InitOnce();
     MallocHooks::ResetStats();
   }
@@ -53,6 +52,7 @@ class EnableMallocHooksAndStacksScope : public EnableMallocHooksScope {
       FLAG_profiler = true;
       Profiler::InitOnce();
     }
+    MallocHooks::ResetStats();
   }
 
   ~EnableMallocHooksAndStacksScope() {