disallow left-trim fast path when sampling heap profiler is active

test/cctest/test-heap-profiler.cc

Index: test/cctest/test-heap-profiler.cc
diff --git a/test/cctest/test-heap-profiler.cc b/test/cctest/test-heap-profiler.cc
index eeb722c7fb5e405544be8c363dc21fa3bb6c5827..914c1f987dbdb3edc77953d6699052523b8d022b 100644
--- a/test/cctest/test-heap-profiler.cc
+++ b/test/cctest/test-heap-profiler.cc
@@ -3040,3 +3040,26 @@ TEST(SamplingHeapProfilerApiAllocation) {
 
   heap_profiler->StopSamplingHeapProfiler();
 }
+
+TEST(SamplingHeapProfilerLeftTrimming) {
+  v8::HandleScope scope(v8::Isolate::GetCurrent());
+  LocalContext env;
+  v8::HeapProfiler* heap_profiler = env->GetIsolate()->GetHeapProfiler();
+
+  // Suppress randomness to avoid flakiness in tests.
+  v8::internal::FLAG_sampling_heap_profiler_suppress_randomness = true;
+
+  heap_profiler->StartSamplingHeapProfiler(64);
+
+  CompileRun(
+      "for (var j = 0; j < 30000; ++j) {\n"
+      "  var a = [];\n"
+      "  for (var i = 0; i < 5; ++i)\n"
+      "      a[i] = i;\n"
+      "  for (var i = 0; i < 3; ++i)\n"
+      "      a.shift();\n"
+      "}\n");
+  // Should not crash.

[Hannes Payer (out of office), 2016/04/13 13:32:29]

Don't you need to call GC to crash? Why does it crash right now?

+
+  heap_profiler->StopSamplingHeapProfiler();
+}