[inspector] An Error with no stack description should not be empty

Make the description return the class name as it used to be.

BUG=chromium:919292

Change-Id: Idbc07643f15014a39a08a545a5003be891d95bd3
Reviewed-on: https://chromium-review.googlesource.com/c/1416318Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58867}

src/inspector/value-mirror.cc

@@ -205,7 +205,7 @@ String16 descriptionForError(v8::Local<v8::Context> context,
   if (!object->Get(context, toV8String(isolate, "stack"))
            .ToLocal(&stackValue) ||
       !stackValue->IsString()) {
-    return String16();
+    return className;
   }
   String16 stack = toProtocolString(isolate, stackValue.As<v8::String>());
   String16 description = stack;

test/inspector/runtime/remote-object-expected.txt

@@ -1424,6 +1424,18 @@ Running test: testError
     }
 }
 
+Running test: testCustomError
+'class CustomError extends Error {}; a = new CustomError(); delete a.stack; a', returnByValue: false, generatePreview: false
+{
+    result : {
+        className : CustomError
+        description : CustomError
+        objectId : <objectId>
+        subtype : error
+        type : object
+    }
+}
+
 Running test: testProxy
 'new Proxy({}, {})', returnByValue: false, generatePreview: false
 {

test/inspector/runtime/remote-object.js

@@ -414,6 +414,11 @@ InspectorTest.runAsyncTestSuite([
       returnByValue: true
     })).result);
   },
+  async function testCustomError() {
+    InspectorTest.logMessage((await evaluate({
+      expression: `class CustomError extends Error {}; a = new CustomError(); delete a.stack; a`
+    })).result);
+  },
   async function testProxy() {
     InspectorTest.logMessage((await evaluate({
       expression: 'new Proxy({}, {})'