Fix test-cpu-profiler/FunctionCallSample flakiness under GC stress testing

test/cctest/test-cpu-profiler.cc

Index: test/cctest/test-cpu-profiler.cc
diff --git a/test/cctest/test-cpu-profiler.cc b/test/cctest/test-cpu-profiler.cc
index 223f5fc3925057dc70e228c8a39520c45972260b..36961a9709875933b4a0aec7237f3fcbba625f3f 100644
--- a/test/cctest/test-cpu-profiler.cc
+++ b/test/cctest/test-cpu-profiler.cc
@@ -1087,8 +1087,14 @@ TEST(FunctionCallSample) {
     CheckChildrenNames(root, names);
   }
 
-  const v8::CpuProfileNode* startNode = GetChild(root, "start");
-  {
+  // In case of GC stress tests all samples may be in GC phase and there
+  // won't be |start| node in the profiles.
+  bool start_node_must_exist =
+      (i::FLAG_gc_interval == -1) && !i::FLAG_stress_compaction;
+  const v8::CpuProfileNode* startNode = start_node_must_exist
+                                      ? GetChild(root, "start")
+                                      : FindChild(root, "start");
+  if (startNode) {
     ScopedVector<v8::Handle<v8::String> > names(1);
     names[0] = v8::String::New("bar");
     CheckChildrenNames(startNode, names);