lint unnecessary_new on samples (#21539)

* lint unnecessary_new on samples

* fix tests

dev/bots/analyze-sample-code.dart

diff --git a/dev/bots/analyze-sample-code.dart b/dev/bots/analyze-sample-code.dart
index a3087b7..8662d33 100644
--- a/dev/bots/analyze-sample-code.dart
+++ b/dev/bots/analyze-sample-code.dart
@@ -218,6 +218,7 @@
 linter:
   rules:
     - unnecessary_const
+    - unnecessary_new
 ''');
     print('Found $sampleCodeSections sample code sections.');
     final Process process = await Process.start(
@@ -314,18 +315,20 @@
   exit(exitCode);
 }
 
+final RegExp _constructorRegExp = new RegExp(r'[A-Z][a-zA-Z0-9<>.]*\(');
+
 int _expressionId = 0;
 
 void processBlock(Line line, List<String> block, List<Section> sections) {
   if (block.isEmpty)
     throw '$line: Empty ```dart block in sample code.';
-  if (block.first.startsWith('new ') || block.first.startsWith('const ')) {
+  if (block.first.startsWith('new ') || block.first.startsWith('const ') || block.first.startsWith(_constructorRegExp)) {
     _expressionId += 1;
     sections.add(new Section(line, 'dynamic expression$_expressionId = ', block.toList(), ';'));
   } else if (block.first.startsWith('await ')) {
     _expressionId += 1;
     sections.add(new Section(line, 'Future<Null> expression$_expressionId() async { ', block.toList(), ' }'));
-  } else if (block.first.startsWith('class ')) {
+  } else if (block.first.startsWith('class ') || block.first.startsWith('enum ')) {
     sections.add(new Section(line, null, block.toList(), null));
   } else {
     final List<String> buffer = <String>[];

dev/bots/test/analyze-sample-code_test.dart

diff --git a/dev/bots/test/analyze-sample-code_test.dart b/dev/bots/test/analyze-sample-code_test.dart
index 0774eea..8eb1f11 100644
--- a/dev/bots/test/analyze-sample-code_test.dart
+++ b/dev/bots/test/analyze-sample-code_test.dart
@@ -30,8 +30,10 @@
       "$directory/main.dart:5:8: Unused import: 'dart:ui'",
       "$directory/main.dart:6:8: Unused import: 'package:flutter_test/flutter_test.dart'",
       "$directory/main.dart:9:8: Target of URI doesn't exist: 'package:flutter/known_broken_documentation.dart'",
+      'test/analyze-sample-code-test-input/known_broken_documentation.dart:27:5: Unnecessary new keyword (unnecessary_new)',
       "test/analyze-sample-code-test-input/known_broken_documentation.dart:27:9: Undefined class 'Opacity' (undefined_class)",
       "test/analyze-sample-code-test-input/known_broken_documentation.dart:29:20: Undefined class 'Text' (undefined_class)",
+      'test/analyze-sample-code-test-input/known_broken_documentation.dart:39:5: Unnecessary new keyword (unnecessary_new)',
       "test/analyze-sample-code-test-input/known_broken_documentation.dart:39:9: Undefined class 'Opacity' (undefined_class)",
       "test/analyze-sample-code-test-input/known_broken_documentation.dart:41:20: Undefined class 'Text' (undefined_class)",
       'test/analyze-sample-code-test-input/known_broken_documentation.dart:42:5: unexpected comma at end of sample code',