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

test/cctest/test-cpu-profiler.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 //
 // Tests of profiles generator and utilities.
 
 #ifdef ENABLE_LOGGING_AND_PROFILING
 
 #include "v8.h"
 #include "cpu-profiler-inl.h"
 #include "cctest.h"
 
 namespace i = v8::internal;
 
 using i::CodeEntry;
 using i::CpuProfile;
+using i::CpuProfiler;
 using i::CpuProfilesCollection;
 using i::ProfileGenerator;
 using i::ProfileNode;
 using i::ProfilerEventsProcessor;
 using i::TokenEnumerator;
 
 
 TEST(StartStop) {
   CpuProfilesCollection profiles;
   ProfileGenerator generator(&profiles);
@@ skipping 193 matching lines @@
   const i::List<ProfileNode*>* bottom_up_ddd_children =
       bottom_up_root_children[2]->children();
   CHECK_EQ(1, bottom_up_ddd_children->length());
   CHECK_EQ("5", bottom_up_ddd_children->last()->entry()->name());
   const i::List<ProfileNode*>* bottom_up_ddd_stub_children =
       bottom_up_ddd_children->last()->children();
   CHECK_EQ(1, bottom_up_ddd_stub_children->length());
   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