Fix CPU profiler crash in start / stop sequence when non-existent name is passed

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 0e6f09d2ef0159c6aff2b0d8cebf0fc5e8c79fb8..239d8ae695106745f108324d914e09c2d5917a40 100644
--- a/test/cctest/test-cpu-profiler.cc
+++ b/test/cctest/test-cpu-profiler.cc
@@ -12,6 +12,7 @@ namespace i = v8::internal;
 
 using i::CodeEntry;
 using i::CpuProfile;
+using i::CpuProfiler;
 using i::CpuProfilesCollection;
 using i::ProfileGenerator;
 using i::ProfileNode;
@@ -225,4 +226,18 @@ TEST(TickEvents) {
   CHECK_EQ("bbb", bottom_up_ddd_stub_children->last()->entry()->name());
 }
 
+
+// http://crbug/51594
+// This test must not crash.
+TEST(CrashIfStoppingLastNonExistentProfile) {
+  InitializeVM();
+  TestSetup test_setup;
+  CpuProfiler::Setup();
+  CpuProfiler::StartProfiling("1");
+  CpuProfiler::StopProfiling("2");
+  CpuProfiler::StartProfiling("1");
+  CpuProfiler::StopProfiling("");
+  CpuProfiler::TearDown();
+}
+
 #endif  // ENABLE_LOGGING_AND_PROFILING