Add spell-checking to `gn help`.

tools/gn/string_utils_unittest.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "tools/gn/string_utils.h"
 
 #include <stdint.h>
 #include <utility>
 
 #include "testing/gtest/include/gtest/gtest.h"
@@ skipping 93 matching lines @@
   EXPECT_TRUE(CheckExpansionCase("hello #${onescope.two}", nullptr, false));
 
   // Accessing the list.
   EXPECT_TRUE(CheckExpansionCase("hello #${onelist[0]}", "hello #1", true));
   EXPECT_TRUE(CheckExpansionCase("hello #${onelist[1]}", nullptr, false));
 
   // Trying some other (otherwise valid) expressions should fail.
   EXPECT_TRUE(CheckExpansionCase("${1 + 2}", nullptr, false));
   EXPECT_TRUE(CheckExpansionCase("${print(1)}", nullptr, false));
 }
+
+TEST(StringUtils, EditDistance) {
+  EXPECT_EQ(3u, EditDistance("doom melon", "dune melon", 100));
+  EXPECT_EQ(2u, EditDistance("doom melon", "dune melon", 1));
+
+  EXPECT_EQ(2u, EditDistance("ab", "ba", 100));
+  EXPECT_EQ(2u, EditDistance("ba", "ab", 100));
+
+  EXPECT_EQ(2u, EditDistance("ananas", "banana", 100));
+  EXPECT_EQ(2u, EditDistance("banana", "ananas", 100));
+
+  EXPECT_EQ(2u, EditDistance("unclear", "nuclear", 100));
+  EXPECT_EQ(2u, EditDistance("nuclear", "unclear", 100));
+
+  EXPECT_EQ(3u, EditDistance("chrome", "chromium", 100));
+  EXPECT_EQ(3u, EditDistance("chromium", "chrome", 100));
+
+  EXPECT_EQ(4u, EditDistance("", "abcd", 100));
+  EXPECT_EQ(4u, EditDistance("abcd", "", 100));
+
+  EXPECT_EQ(4u, EditDistance("xxx", "xxxxxxx", 100));
+  EXPECT_EQ(4u, EditDistance("xxxxxxx", "xxx", 100));
+
+  EXPECT_EQ(7u, EditDistance("yyy", "xxxxxxx", 100));
+  EXPECT_EQ(7u, EditDistance("xxxxxxx", "yyy", 100));
+}
+
+TEST(StringUtils, SpellcheckString) {
+  std::vector<base::StringPiece> words;
+  words.push_back("your");
+  words.push_back("bravado");
+  words.push_back("won\'t");
+  words.push_back("help");
+  words.push_back("you");
+  words.push_back("now");
+
+  EXPECT_EQ("help", SpellcheckString("halp", words));
+
+  // barbados has an edit distance of 4 from bravado, so there's no suggestion.
+  EXPECT_TRUE(SpellcheckString("barbados", words).empty());
+}