[debugger] correctly find function context.

test/mjsunit/regress/regress-crbug-582051.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: --expose-debug-as debug
+
+var test_y = false;
+
+function foo(a = 1) {
+  var x = 2;
+  debugger;
+  eval("var y = 3");
+  test_y = true;
+  debugger;
+}
+
+var exception = null;
+var break_count = 0;
+var Debug = debug.Debug;
+var ScopeType = debug.ScopeType;
+
+function listener(event, exec_state) {
+  if (event != Debug.DebugEvent.Break) return;
+  try {
+    var scopes = exec_state.frame(0).allScopes();
+    var expectation = [ ScopeType.Block,
+                        ScopeType.Local,
+                        ScopeType.Script,
+                        ScopeType.Global ];
+    assertEquals(expectation, scopes.map(x => x.scopeType()));
+    assertEquals(2, scopes[0].scopeObject().value().x);
+    if (test_y) assertEquals(3, scopes[0].scopeObject().value().y);
+    assertEquals(1, scopes[1].scopeObject().value().a);
+    break_count++;
+  } catch (e) {
+    print(e);
+    exception = e;
+  }
+}
+Debug.setListener(listener);
+foo();
+
+assertNull(exception);
+assertEquals(2, break_count);