[debugger] do not accidentally pop contexts in bytecode

R=jgruber@chromium.org, mstarzinger@chromium.org
BUG=v8:5610

Review-Url: https://codereview.chromium.org/2482133002
Cr-Commit-Position: refs/heads/master@{#40827}

src/interpreter/bytecode-generator.cc

@@ -362,7 +362,7 @@ void BytecodeGenerator::ControlScope::PerformCommand(Command command,
       return;
     }
     current = current->outer();
-    if (current->context() != context) {
+    if (current->context() != context && context->ShouldPopContext()) {
       // Pop context to the expected depth.
       // TODO(rmcilroy): Only emit a single context pop.
       generator()->builder()->PopContext(current->context()->reg());

test/debugger/regress/regress-5610.js

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-async-await --turbo
+
+var Debug = debug.Debug;
+var step_count = 0;
+
+function listener(event, execState, eventData, data) {
+  if (event != Debug.DebugEvent.Break) return;
+  try {
+    var line = execState.frame(0).sourceLineText();
+    print(line);
+    var [match, expected_count, step] = /\/\/ B(\d) (\w+)$/.exec(line);
+    assertEquals(step_count++, parseInt(expected_count));
+    if (step != "Continue") execState.prepareStep(Debug.StepAction[step]);
+  } catch (e) {
+    print(e, e.stack);
+    quit(1);
+  }
+}
+
+Debug.setListener(listener);
+
+async function f() {
+  var a = 1;
+  debugger;          // B0 StepNext
+  print(1);          // B1 StepNext
+  return a;          // B2 StepNext
+}                    // B3 Continue
+
+f();