inspector: simplify preview generator for Error objects

- we can avoid using regexps,
- this CL also fixed a bug.

R=alph@chromium.org

Bug: chromium:870957
Cq-Include-Trybots: luci.chromium.try:linux_chromium_headless_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I9799507b85942be454a7c20d2768fe7442fc965e
Reviewed-on: https://chromium-review.googlesource.com/1250403
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56295}

src/inspector/injected-script-source.js

@@ -661,16 +661,15 @@ InjectedScript.prototype = {
 
         if (InjectedScriptHost.subtype(obj) === "error") {
             try {
-                var stack = obj.stack;
-                var message = obj.message && obj.message.length ? ": " + obj.message : "";
-                var firstCallFrame = /^\s+at\s/m.exec(stack);
-                var stackMessageEnd = firstCallFrame ? firstCallFrame.index : -1;
-                if (stackMessageEnd !== -1) {
-                    var stackTrace = stack.substr(stackMessageEnd);
-                    return className + message + "\n" + stackTrace;
-                }
-                return className + message;
+                const stack = obj.stack;
+                if (stack.substr(0, className.length) === className)
+                    return stack;
+                const message = obj.message;
+                const index = /* suppressBlacklist */ stack.indexOf(message);
+                const messageWithStack = index !== -1 ? stack.substr(index) : message;
+                return className + ': ' + messageWithStack;
             } catch(e) {
+                return className;
             }
         }
 

test/inspector/runtime/error-preview-expected.txt

+Checks preview for Error object
+{
+    className : TypeError
+    description : TypeError: [].     at is not a function     at <anonymous>:1:15
+    objectId : <objectId>
+    subtype : error
+    type : object
+}

test/inspector/runtime/error-preview.js

+// Copyright 2018 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.
+
+const {session, contextGroup, Protocol} = InspectorTest.start(
+    'Checks preview for Error object');
+
+(async function test() {
+  const { result: { result } } = await Protocol.Runtime.evaluate({
+    expression: `[]['\\n    at']()`,
+    generatePreview: true
+  });
+  InspectorTest.logMessage(result);
+  InspectorTest.completeTest();
+})()