Fixed issue in MallocHooks where a MallocHookScope was accidentally removed during a merge, causing…

runtime/vm/snapshot_test.cc

Index: runtime/vm/snapshot_test.cc
diff --git a/runtime/vm/snapshot_test.cc b/runtime/vm/snapshot_test.cc
index a910b54589747513225431ad0d48cab2c5e8fc65..41953ecee96db15980da18dc1804dd51070268e1 100644
--- a/runtime/vm/snapshot_test.cc
+++ b/runtime/vm/snapshot_test.cc
@@ -12,6 +12,7 @@
 #include "vm/dart_api_message.h"
 #include "vm/dart_api_state.h"
 #include "vm/flags.h"
+#include "vm/malloc_hooks.h"
 #include "vm/snapshot.h"
 #include "vm/symbols.h"
 #include "vm/unicode.h"
@@ -1122,6 +1123,11 @@ static void IterateScripts(const Library& lib) {
 }
 
 ISOLATE_UNIT_TEST_CASE(GenerateSource) {
+  // Disable stack trace collection for this test as it results in a timeout.
+  bool stack_trace_collection_enabled =
+      MallocHooks::stack_trace_collection_enabled();
+  MallocHooks::set_stack_trace_collection_enabled(false);
+
   Zone* zone = thread->zone();
   Isolate* isolate = thread->isolate();
   const GrowableObjectArray& libs =
@@ -1135,6 +1141,9 @@ ISOLATE_UNIT_TEST_CASE(GenerateSource) {
     OS::Print("Generating source for library: %s\n", uri.ToCString());
     IterateScripts(lib);
   }
+
+  MallocHooks::set_stack_trace_collection_enabled(
+      stack_trace_collection_enabled);
 }