Do not reflect uninitialized 'let' and 'const' in scope mirrors.

R=yangguo@chromium.org,aandrey@chromium.org
BUG=v8:3743
LOG=N

Review URL: https://codereview.chromium.org/758603004

Cr-Commit-Position: refs/heads/master@{#25712}

src/scopeinfo.cc

@@ -380,13 +380,14 @@ bool ScopeInfo::CopyContextLocalsToScopeObject(Handle<ScopeInfo> scope_info,
   for (int i = 0; i < local_count; ++i) {
     if (scope_info->LocalIsSynthetic(first_context_var + i)) continue;
     int context_index = Context::MIN_CONTEXT_SLOTS + i;
+    Handle<Object> value = Handle<Object>(context->get(context_index), isolate);
+    // Do not reflect variables under TDZ in scope object.
+    if (value->IsTheHole()) continue;
     RETURN_ON_EXCEPTION_VALUE(
-        isolate,
-        Runtime::DefineObjectProperty(
-            scope_object,
-            Handle<String>(String::cast(scope_info->get(i + start))),
-            Handle<Object>(context->get(context_index), isolate),
-            ::NONE),
+        isolate, Runtime::DefineObjectProperty(
+                     scope_object,
+                     Handle<String>(String::cast(scope_info->get(i + start))),
+                     value, ::NONE),
         false);
   }
   return true;

test/mjsunit/harmony/debug-blockscopes.js

@@ -481,3 +481,24 @@ listener_delegate = function(exec_state) {
 };
 for_loop_5();
 EndTest();
+
+
+// Uninitialized variables
+BeginTest("Uninitialized 1");
+
+function uninitialized_1() {
+  {
+    debugger;
+    let x = 1;
+  }
+}
+
+listener_delegate = function(exec_state) {
+  CheckScopeChain([debug.ScopeType.Block,
+                   debug.ScopeType.Local,
+                   debug.ScopeType.Script,
+                   debug.ScopeType.Global], exec_state);
+  CheckScopeContent({}, 0, exec_state);
+};
+uninitialized_1();
+EndTest();