Allow string::front() and back() and update the codebase to use back().

I searched for "length() - 1]", which won't find all potential sites to use
back(), but should hit a reasonable number.  These were all converted.

I don't consider str.front() to be vastly more readable than str[0], so I made
no effort to seek these out and change them.  I did change code to use front()
when it would make for better parallel structure with a place I was making use
back(), e.g.:

if (str[0] == 'x' && str[str.length() - 1] == 'y') {

...was transformed to:

if (str.front() == 'x' && str.back() == 'y') {

...and not:

if (str[0] == 'x' && str.back() == 'y') {

I also added front() and back() methods to StringPiece so people wouldn't need to distinguish between string and StringPiece for these purposes.

BUG=none
TEST=none

Review URL: https://codereview.chromium.org/1663253004

Cr-Commit-Position: refs/heads/master@{#373672}

37 files changed, 62 insertions, 63 deletions

diff --git a/base/files/file_path.cc b/base/files/file_path.cc
index 63e9387..5756dfc 100644
--- a/base/files/file_path.cc
+++ b/base/files/file_path.cc
@@ -502,10 +502,10 @@ FilePath FilePath::Append(StringPieceType component) const {
   // Don't append a separator if the path is empty (indicating the current
   // directory) or if the path component is empty (indicating nothing to
   // append).
-  if (appended.length() > 0 && new_path.path_.length() > 0) {
+  if (!appended.empty() && !new_path.path_.empty()) {
     // Don't append a separator if the path still ends with a trailing
     // separator after stripping (indicating the root directory).
-    if (!IsSeparator(new_path.path_[new_path.path_.length() - 1])) {
+    if (!IsSeparator(new_path.path_.back())) {
       // Don't append a separator if the path is just a drive letter.
       if (FindDriveLetter(new_path.path_) + 1 != new_path.path_.length()) {
         new_path.path_.append(1, kSeparators[0]);
diff --git a/base/mac/foundation_util.mm b/base/mac/foundation_util.mm
index 524f17c..6ae5df3 100644
--- a/base/mac/foundation_util.mm
+++ b/base/mac/foundation_util.mm
@@ -165,7 +165,7 @@ FilePath GetAppBundlePath(const FilePath& exec_name) {
 
   // The first component may be "/" or "//", etc. Only append '/' if it doesn't
   // already end in '/'.
-  if (bundle_name[bundle_name.length() - 1] != '/')
+  if (bundle_name.back() != '/')
     bundle_name += '/';
 
   // Go through the remaining components.
diff --git a/base/strings/string_piece.h b/base/strings/string_piece.h
index 92634b9..20784d7 100644
--- a/base/strings/string_piece.h
+++ b/base/strings/string_piece.h
@@ -224,6 +224,8 @@ template <typename STRING_TYPE> class BasicStringPiece {
   }
 
   value_type operator[](size_type i) const { return ptr_[i]; }
+  value_type front() const { return ptr_[0]; }
+  value_type back() const { return ptr_[length_ - 1]; }
 
   void remove_prefix(size_type n) {
     ptr_ += n;
diff --git a/base/sys_info_linux.cc b/base/sys_info_linux.cc
index 8e1f533..300ef2c0 100644
--- a/base/sys_info_linux.cc
+++ b/base/sys_info_linux.cc
@@ -37,7 +37,7 @@ uint64_t MaxSharedMemorySize() {
   std::string contents;
   base::ReadFileToString(base::FilePath("/proc/sys/kernel/shmmax"), &contents);
   DCHECK(!contents.empty());
-  if (!contents.empty() && contents[contents.length() - 1] == '\n') {
+  if (!contents.empty() && contents.back() == '\n') {
     contents.erase(contents.length() - 1);
   }
 
diff --git a/chrome/browser/browsing_data/cookies_tree_model_unittest.cc b/chrome/browser/browsing_data/cookies_tree_model_unittest.cc
index ac1724c..22f0766 100644
--- a/chrome/browser/browsing_data/cookies_tree_model_unittest.cc
+++ b/chrome/browser/browsing_data/cookies_tree_model_unittest.cc
@@ -353,7 +353,7 @@ class CookiesTreeModelTest : public testing::Test {
     CookieTreeRootNode* root = static_cast<CookieTreeRootNode*>(
         cookies_model->GetRoot());
     std::string retval = GetNodesOfChildren(root, type);
-    if (retval.length() && retval[retval.length() - 1] == ',')
+    if (!retval.empty() && retval.back() == ',')
       retval.erase(retval.length() - 1);
     return retval;
   }
diff --git a/chrome/browser/extensions/extension_creator_filter.cc b/chrome/browser/extensions/extension_creator_filter.cc
index 330557f2..85efaa1 100644
--- a/chrome/browser/extensions/extension_creator_filter.cc
+++ b/chrome/browser/extensions/extension_creator_filter.cc
@@ -45,9 +45,8 @@ bool ExtensionCreatorFilter::ShouldPackageFile(
       return false;
   }
 
-  base::FilePath::CharType first_character = base_name.value()[0];
-  base::FilePath::CharType last_character =
-      base_name.value()[base_name.value().length() - 1];
+  base::FilePath::CharType first_character = base_name.value().front();
+  base::FilePath::CharType last_character = base_name.value().back();
 
   // dotfile
   if (first_character == '.') {
diff --git a/chrome/browser/policy/policy_path_parser_linux.cc b/chrome/browser/policy/policy_path_parser_linux.cc
index 6dc2af4..9b0e6fd 100644
--- a/chrome/browser/policy/policy_path_parser_linux.cc
+++ b/chrome/browser/policy/policy_path_parser_linux.cc
@@ -27,8 +27,8 @@ base::FilePath::StringType ExpandPathVariables(
     return result;
   // Sanitize quotes in case of any around the whole string.
   if (result.length() > 1 &&
-      ((result[0] == '"' && result[result.length() - 1] == '"') ||
-      (result[0] == '\'' && result[result.length() - 1] == '\''))) {
+      ((result.front() == '"' && result.back() == '"') ||
+       (result.front() == '\'' && result.back() == '\''))) {
     // Strip first and last char which should be matching quotes now.
     result = result.substr(1, result.length() - 2);
   }
diff --git a/chrome/browser/policy/policy_path_parser_mac.mm b/chrome/browser/policy/policy_path_parser_mac.mm
index 1ac9558..24275f6 100644
--- a/chrome/browser/policy/policy_path_parser_mac.mm
+++ b/chrome/browser/policy/policy_path_parser_mac.mm
@@ -48,8 +48,8 @@ base::FilePath::StringType ExpandPathVariables(
     return result;
   // Sanitize quotes in case of any around the whole string.
   if (result.length() > 1 &&
-      ((result[0] == '"' && result[result.length() - 1] == '"') ||
-      (result[0] == '\'' && result[result.length() - 1] == '\''))) {
+      ((result.front() == '"' && result.back() == '"') ||
+       (result.front() == '\'' && result.back() == '\''))) {
     // Strip first and last char which should be matching quotes now.
     result = result.substr(1, result.length() - 2);
   }
diff --git a/chrome/browser/policy/policy_path_parser_win.cc b/chrome/browser/policy/policy_path_parser_win.cc
index d8c62c7..6a1888d 100644
--- a/chrome/browser/policy/policy_path_parser_win.cc
+++ b/chrome/browser/policy/policy_path_parser_win.cc
@@ -73,8 +73,8 @@ base::FilePath::StringType ExpandPathVariables(
     return result;
   // Sanitize quotes in case of any around the whole string.
   if (result.length() > 1 &&
-      ((result[0] == L'"' && result[result.length() - 1] == L'"') ||
-       (result[0] == L'\'' && result[result.length() - 1] == L'\''))) {
+      ((result.front() == L'"' && result.back() == L'"') ||
+       (result.front() == L'\'' && result.back() == L'\''))) {
     // Strip first and last char which should be matching quotes now.
     result = result.substr(1, result.length() - 2);
   }
diff --git a/chrome/common/cloud_print/cloud_print_helpers.cc b/chrome/common/cloud_print/cloud_print_helpers.cc
index 6fcd8bd..a5a450e 100644
--- a/chrome/common/cloud_print/cloud_print_helpers.cc
+++ b/chrome/common/cloud_print/cloud_print_helpers.cc
@@ -52,7 +52,7 @@ std::string HashPrinterTags(const PrinterTags& printer_tags) {
 std::string AppendPathToUrl(const GURL& url, const std::string& path) {
   DCHECK_NE(path[0], '/');
   std::string ret = url.path();
-  if (url.has_path() && (ret[ret.length() - 1] != '/'))
+  if (url.has_path() && (ret.back() != '/'))
     ret += '/';
   ret += path;
   return ret;
diff --git a/chrome/common/cloud_print/cloud_print_helpers_unittest.cc b/chrome/common/cloud_print/cloud_print_helpers_unittest.cc
index 41b8f98..2792218 100644
--- a/chrome/common/cloud_print/cloud_print_helpers_unittest.cc
+++ b/chrome/common/cloud_print/cloud_print_helpers_unittest.cc
@@ -17,7 +17,7 @@ namespace {
 
 void CheckURLs(const GURL& server_base_url) {
   std::string expected_url_base = server_base_url.spec();
-  if (expected_url_base[expected_url_base.length() - 1] != '/')
+  if (expected_url_base.back() != '/')
     expected_url_base += "/";
 
   EXPECT_EQ(base::StringPrintf("%ssearch", expected_url_base.c_str()),
diff --git a/chrome/service/cloud_print/cloud_print_service_helpers_unittest.cc b/chrome/service/cloud_print/cloud_print_service_helpers_unittest.cc
index 761e18f..b41fb08 100644
--- a/chrome/service/cloud_print/cloud_print_service_helpers_unittest.cc
+++ b/chrome/service/cloud_print/cloud_print_service_helpers_unittest.cc
@@ -16,7 +16,7 @@ namespace {
 
 void CheckJobStatusURLs(const GURL& server_base_url) {
   std::string expected_url_base = server_base_url.spec();
-  if (expected_url_base[expected_url_base.length() - 1] != '/')
+  if (expected_url_base.back() != '/')
     expected_url_base += "/";
 
   EXPECT_EQ(base::StringPrintf(
diff --git a/chrome/test/chromedriver/server/chromedriver_server.cc b/chrome/test/chromedriver/server/chromedriver_server.cc
index 3158795..61db7c4 100644
--- a/chrome/test/chromedriver/server/chromedriver_server.cc
+++ b/chrome/test/chromedriver/server/chromedriver_server.cc
@@ -285,9 +285,9 @@ int main(int argc, char *argv[]) {
   }
   if (cmd_line->HasSwitch("url-base"))
     url_base = cmd_line->GetSwitchValueASCII("url-base");
-  if (url_base.empty() || url_base[0] != '/')
+  if (url_base.empty() || url_base.front() != '/')
     url_base = "/" + url_base;
-  if (url_base[url_base.length() - 1] != '/')
+  if (url_base.back() != '/')
     url_base = url_base + "/";
   if (cmd_line->HasSwitch("whitelisted-ips")) {
     allow_remote = true;
diff --git a/chromeos/disks/disk_mount_manager.cc b/chromeos/disks/disk_mount_manager.cc
index 3c89ac6..d4edfea 100644
--- a/chromeos/disks/disk_mount_manager.cc
+++ b/chromeos/disks/disk_mount_manager.cc
@@ -275,7 +275,7 @@ class DiskMountManagerImpl : public DiskMountManager {
   void UnmountChildMounts(const std::string& mount_path_in) {
     std::string mount_path = mount_path_in;
     // Let's make sure mount path has trailing slash.
-    if (mount_path[mount_path.length() - 1] != '/')
+    if (mount_path.back() != '/')
       mount_path += '/';
 
     for (MountPointMap::iterator it = mount_points_.begin();
diff --git a/components/autofill/core/browser/webdata/autofill_table.cc b/components/autofill/core/browser/webdata/autofill_table.cc
index cc4f6a8..07a291c 100644
--- a/components/autofill/core/browser/webdata/autofill_table.cc
+++ b/components/autofill/core/browser/webdata/autofill_table.cc
@@ -495,7 +495,7 @@ bool AutofillTable::GetFormValuesForElementName(
   } else {
     base::string16 prefix_lower = base::i18n::ToLower(prefix);
     base::string16 next_prefix = prefix_lower;
-    next_prefix[next_prefix.length() - 1]++;
+    next_prefix.back()++;
 
     sql::Statement s1;
     s1.Assign(db_->GetUniqueStatement(
diff --git a/components/metrics/serialization/serialization_utils_unittest.cc b/components/metrics/serialization/serialization_utils_unittest.cc
index 9c8f9de..fe8f2b2 100644
--- a/components/metrics/serialization/serialization_utils_unittest.cc
+++ b/components/metrics/serialization/serialization_utils_unittest.cc
@@ -32,7 +32,7 @@ class SerializationUtilsTest : public testing::Test {
 
   void TestSerialization(MetricSample* sample) {
     std::string serialized(sample->ToString());
-    ASSERT_EQ('\0', serialized[serialized.length() - 1]);
+    ASSERT_EQ('\0', serialized.back());
     scoped_ptr<MetricSample> deserialized =
         SerializationUtils::ParseSample(serialized);
     ASSERT_TRUE(deserialized);
diff --git a/components/omnibox/browser/history_provider.cc b/components/omnibox/browser/history_provider.cc
index 004d542..367d243 100644
--- a/components/omnibox/browser/history_provider.cc
+++ b/components/omnibox/browser/history_provider.cc
@@ -38,8 +38,7 @@ void HistoryProvider::DeleteMatch(const AutocompleteMatch& match) {
 bool HistoryProvider::PreventInlineAutocomplete(
     const AutocompleteInput& input) {
   return input.prevent_inline_autocomplete() ||
-      (!input.text().empty() &&
-       base::IsUnicodeWhitespace(input.text()[input.text().length() - 1]));
+      (!input.text().empty() && base::IsUnicodeWhitespace(input.text().back()));
 }
 
 HistoryProvider::HistoryProvider(AutocompleteProvider::Type type,
diff --git a/components/search_engines/template_url_service.cc b/components/search_engines/template_url_service.cc
index 40d2008..0e944ac 100644
--- a/components/search_engines/template_url_service.cc
+++ b/components/search_engines/template_url_service.cc
@@ -352,8 +352,8 @@ base::string16 TemplateURLService::CleanUserInputKeyword(
   result = url_formatter::StripWWW(result);
 
   // Remove trailing "/".
-  return (result.length() > 0 && result[result.length() - 1] == '/') ?
-      result.substr(0, result.length() - 1) : result;
+  return (result.empty() || result.back() != '/') ?
+      result : result.substr(0, result.length() - 1);
 }
 
 bool TemplateURLService::CanAddAutogeneratedKeyword(
diff --git a/content/child/multipart_response_delegate.cc b/content/child/multipart_response_delegate.cc
index 4e1841e..9e9bb9c 100644
--- a/content/child/multipart_response_delegate.cc
+++ b/content/child/multipart_response_delegate.cc
@@ -176,7 +176,7 @@ void MultipartResponseDelegate::OnReceivedData(const char* data,
     // If the last character is a new line character, go ahead and just send
     // everything we have buffered.  This matches an optimization in Gecko.
     int send_length = data_.length() - boundary_.length();
-    if (data_[data_.length() - 1] == '\n')
+    if (data_.back() == '\n')
       send_length = data_.length();
     if (client_)
       client_->didReceiveData(loader_,
diff --git a/extensions/common/permissions/socket_permission_entry.cc b/extensions/common/permissions/socket_permission_entry.cc
index fdb6de8..a6fbb3b 100644
--- a/extensions/common/permissions/socket_permission_entry.cc
+++ b/extensions/common/permissions/socket_permission_entry.cc
@@ -31,8 +31,8 @@ const uint16_t kWildcardPortNumber = 0;
 const uint16_t kInvalidPort = 65535;
 
 bool StartsOrEndsWithWhitespace(const std::string& str) {
-  return !str.empty() && (base::IsUnicodeWhitespace(str[0]) ||
-                          base::IsUnicodeWhitespace(str[str.length() - 1]));
+  return !str.empty() && (base::IsUnicodeWhitespace(str.front()) ||
+                          base::IsUnicodeWhitespace(str.back()));
 }
 
 }  // namespace
diff --git a/gpu/command_buffer/client/program_info_manager_unittest.cc b/gpu/command_buffer/client/program_info_manager_unittest.cc
index 1911b1c..64d896c 100644
--- a/gpu/command_buffer/client/program_info_manager_unittest.cc
+++ b/gpu/command_buffer/client/program_info_manager_unittest.cc
@@ -206,7 +206,7 @@ TEST_F(ProgramInfoManagerTest, UpdateES2) {
     EXPECT_LT(kNames[0].length(),
               static_cast<size_t>(active_uniform_max_length));
     EXPECT_EQ(kNames[ii], info->name);
-    EXPECT_EQ(kNames[ii][kNames[ii].length() - 1] == ']', info->is_array);
+    EXPECT_EQ(kNames[ii].back() == ']', info->is_array);
     EXPECT_EQ(data.uniforms[ii].size,
               static_cast<int32_t>(info->element_locations.size()));
     for (int32_t uu = 0; uu < data.uniforms[ii].size; ++uu) {
diff --git a/media/filters/video_cadence_estimator_unittest.cc b/media/filters/video_cadence_estimator_unittest.cc
index 939b35c..604a99b 100644
--- a/media/filters/video_cadence_estimator_unittest.cc
+++ b/media/filters/video_cadence_estimator_unittest.cc
@@ -27,8 +27,8 @@ static base::TimeDelta Interval(double hertz) {
 }
 
 std::vector<int> CreateCadenceFromString(const std::string& cadence) {
-  CHECK_EQ('[', cadence[0]);
-  CHECK_EQ(']', cadence[cadence.length() - 1]);
+  CHECK_EQ('[', cadence.front());
+  CHECK_EQ(']', cadence.back());
 
   std::vector<int> result;
   for (const std::string& token :
diff --git a/net/base/filename_util_internal.cc b/net/base/filename_util_internal.cc
index 2f038ad..2b06ee5 100644
--- a/net/base/filename_util_internal.cc
+++ b/net/base/filename_util_internal.cc
@@ -162,8 +162,8 @@ bool IsShellIntegratedExtension(const base::FilePath::StringType& extension) {
   // http://www.juniper.net/security/auto/vulnerabilities/vuln2612.html
   // Files become magical if they end in a CLSID, so block such extensions.
   if (!extension_lower.empty() &&
-      (extension_lower[0] == FILE_PATH_LITERAL('{')) &&
-      (extension_lower[extension_lower.length() - 1] == FILE_PATH_LITERAL('}')))
+      (extension_lower.front() == FILE_PATH_LITERAL('{')) &&
+      (extension_lower.back() == FILE_PATH_LITERAL('}')))
     return true;
   return false;
 }
diff --git a/net/cookies/canonical_cookie.cc b/net/cookies/canonical_cookie.cc
index 34a55af..cdd011f 100644
--- a/net/cookies/canonical_cookie.cc
+++ b/net/cookies/canonical_cookie.cc
@@ -362,8 +362,7 @@ bool CanonicalCookie::IsOnPath(const std::string& url_path) const {
   // the cookie path ends in a trailing '/', or that we prefix up to a '/'
   // in the url path.  Since we know that the url path length is greater
   // than the cookie path length, it's safe to index one byte past.
-  if (path_.length() != url_path.length() &&
-      path_[path_.length() - 1] != '/' &&
+  if (path_.length() != url_path.length() && path_.back() != '/' &&
       url_path[path_.length()] != '/')
     return false;
 
diff --git a/net/cookies/cookie_monster_unittest.cc b/net/cookies/cookie_monster_unittest.cc
index db6b80f..f9d9aeb 100644
--- a/net/cookies/cookie_monster_unittest.cc
+++ b/net/cookies/cookie_monster_unittest.cc
@@ -388,7 +388,7 @@ class CookieMonsterTestBase : public CookieStoreTest<T> {
                            base::SPLIT_WANT_ALL)) {
       DCHECK(!token.empty());
       // Take last character as priority.
-      CookiePriority priority = CharToPriority(token[token.length() - 1]);
+      CookiePriority priority = CharToPriority(token.back());
       std::string priority_str = CookiePriorityToString(priority);
       // The rest of the string (possibly empty) specifies repetition.
       int rep = 1;
diff --git a/net/ftp/ftp_directory_listing_parser_vms.cc b/net/ftp/ftp_directory_listing_parser_vms.cc
index e05f2c7..8139ee0 100644
--- a/net/ftp/ftp_directory_listing_parser_vms.cc
+++ b/net/ftp/ftp_directory_listing_parser_vms.cc
@@ -113,7 +113,7 @@ bool LooksLikeVmsFileProtectionListingPart(const base::string16& input) {
 bool LooksLikeVmsFileProtectionListing(const base::string16& input) {
   if (input.length() < 2)
     return false;
-  if (input[0] != '(' || input[input.length() - 1] != ')')
+  if (input.front() != '(' || input.back() != ')')
     return false;
 
   // We expect four parts of the file protection listing: for System, Owner,
@@ -133,7 +133,7 @@ bool LooksLikeVmsFileProtectionListing(const base::string16& input) {
 bool LooksLikeVmsUserIdentificationCode(const base::string16& input) {
   if (input.length() < 2)
     return false;
-  return input[0] == '[' && input[input.length() - 1] == ']';
+  return input.front() == '[' && input.back() == ']';
 }
 
 bool LooksLikeVMSError(const base::string16& text) {
diff --git a/net/ftp/ftp_network_transaction.cc b/net/ftp/ftp_network_transaction.cc
index 9c2c136..3b31bc1 100644
--- a/net/ftp/ftp_network_transaction.cc
+++ b/net/ftp/ftp_network_transaction.cc
@@ -485,7 +485,7 @@ std::string FtpNetworkTransaction::GetRequestPathForFtpCommand(
   }
   // Make sure that if the path is expected to be a file, it won't end
   // with a trailing slash.
-  if (!is_directory && path.length() > 1 && path[path.length() - 1] == '/')
+  if (!is_directory && path.length() > 1 && path.back() == '/')
     path.erase(path.length() - 1);
   UnescapeRule::Type unescape_rules = UnescapeRule::SPACES |
                                       UnescapeRule::URL_SPECIAL_CHARS;
@@ -886,7 +886,7 @@ int FtpNetworkTransaction::ProcessResponsePWD(const FtpCtrlResponse& response) {
       }
       if (system_type_ == SYSTEM_TYPE_VMS)
         line = FtpUtil::VMSPathToUnix(line);
-      if (line.length() && line[line.length() - 1] == '/')
+      if (!line.empty() && line.back() == '/')
         line.erase(line.length() - 1);
       current_remote_directory_ = line;
       next_state_ = STATE_CTRL_WRITE_TYPE;
diff --git a/net/ftp/ftp_util.cc b/net/ftp/ftp_util.cc
index a2bee15..d7f759c 100644
--- a/net/ftp/ftp_util.cc
+++ b/net/ftp/ftp_util.cc
@@ -82,7 +82,7 @@ std::string FtpUtil::UnixDirectoryPathToVMS(const std::string& unix_path) {
 
   std::string path(unix_path);
 
-  if (path[path.length() - 1] != '/')
+  if (path.back() != '/')
     path.append("/");
 
   // Reuse logic from UnixFilePathToVMS by appending a fake file name to the
@@ -121,7 +121,7 @@ std::string FtpUtil::VMSPathToUnix(const std::string& vms_path) {
   std::replace(result.begin(), result.end(), ']', '/');
 
   // Make sure the result doesn't end with a slash.
-  if (result.length() && result[result.length() - 1] == '/')
+  if (!result.empty() && result.back() == '/')
     result = result.substr(0, result.length() - 1);
 
   return result;
diff --git a/net/proxy/proxy_config_service_linux.cc b/net/proxy/proxy_config_service_linux.cc
index 139e308..314bf71 100644
--- a/net/proxy/proxy_config_service_linux.cc
+++ b/net/proxy/proxy_config_service_linux.cc
@@ -85,7 +85,7 @@ std::string FixupProxyHostScheme(ProxyServer::Scheme scheme,
     host = "socks5://" + host;
   // If there is a trailing slash, remove it so |host| will parse correctly
   // even if it includes a port number (since the slash is not numeric).
-  if (host.length() && host[host.length() - 1] == '/')
+  if (!host.empty() && host.back() == '/')
     host.resize(host.length() - 1);
   return host;
 }
diff --git a/net/tools/balsa/balsa_frame.cc b/net/tools/balsa/balsa_frame.cc
index 8505ac1..37256eb 100644
--- a/net/tools/balsa/balsa_frame.cc
+++ b/net/tools/balsa/balsa_frame.cc
@@ -751,9 +751,9 @@ void ProcessChunkExtensionsManual(base::StringPiece all_extensions,
     SplitStringPiece(extension, '=', &key, &value);
     if (!value.empty()) {
       // Strip quotation marks if they exist.
-      if (!value.empty() && value[0] == '"')
+      if (!value.empty() && value.front() == '"')
         value.remove_prefix(1);
-      if (!value.empty() && value[value.length() - 1] == '"')
+      if (!value.empty() && value.back() == '"')
         value.remove_suffix(1);
     }
 
diff --git a/net/tools/flip_server/url_to_filename_encoder.h b/net/tools/flip_server/url_to_filename_encoder.h
index 583e2fb..c68a9a1 100644
--- a/net/tools/flip_server/url_to_filename_encoder.h
+++ b/net/tools/flip_server/url_to_filename_encoder.h
@@ -108,7 +108,7 @@ class UrlToFilenameEncoder {
 #endif
     } else {
       std::string clean_url(url);
-      if (clean_url.length() && clean_url[clean_url.length() - 1] == '/')
+      if (clean_url.length() && clean_url.back() == '/')
         clean_url.append("index.html");
 
       std::string host = UrlUtilities::GetUrlHost(clean_url);
diff --git a/net/tools/quic/quic_in_memory_cache.cc b/net/tools/quic/quic_in_memory_cache.cc
index 832419e..2dee018 100644
--- a/net/tools/quic/quic_in_memory_cache.cc
+++ b/net/tools/quic/quic_in_memory_cache.cc
@@ -172,7 +172,7 @@ void QuicInMemoryCache::InitializeFromDirectory(const string& cache_directory) {
     size_t path_start = base.find_first_of('/');
     StringPiece host(StringPiece(base).substr(0, path_start));
     StringPiece path(StringPiece(base).substr(path_start));
-    if (path[path.length() - 1] == ',') {
+    if (path.back() == ',') {
       path.remove_suffix(1);
     }
     StringPiece body(file_contents.data() + headers_end,
diff --git a/sandbox/win/src/win_utils.cc b/sandbox/win/src/win_utils.cc
index 3717a97..ef4d803 100644
--- a/sandbox/win/src/win_utils.cc
+++ b/sandbox/win/src/win_utils.cc
@@ -226,7 +226,7 @@ bool SameObject(HANDLE handle, const wchar_t* full_path) {
 
   // This may end with a backslash.
   const wchar_t kBackslash = '\\';
-  if (path[path.length() - 1] == kBackslash)
+  if (path.back() == kBackslash)
     path = path.substr(0, path.length() - 1);
 
   // Perfect match (case-insesitive check).
diff --git a/storage/browser/fileapi/external_mount_points.cc b/storage/browser/fileapi/external_mount_points.cc
index 9fdb4f9..f9ffdbd 100644
--- a/storage/browser/fileapi/external_mount_points.cc
+++ b/storage/browser/fileapi/external_mount_points.cc
@@ -24,7 +24,7 @@ base::FilePath NormalizeFilePath(const base::FilePath& path) {
     return path;
 
   base::FilePath::StringType path_str = path.StripTrailingSeparators().value();
-  if (!base::FilePath::IsSeparator(path_str[path_str.length() - 1]))
+  if (!base::FilePath::IsSeparator(path_str.back()))
     path_str.append(FILE_PATH_LITERAL("/"));
 
   return base::FilePath(path_str).NormalizePathSeparators();
diff --git a/styleguide/c++/c++11.html b/styleguide/c++/c++11.html
index cccae2e..239a282 100644
--- a/styleguide/c++/c++11.html
+++ b/styleguide/c++/c++11.html
@@ -438,6 +438,17 @@ std::end</a></td>
 </tr>
 
 <tr>
+<td>String Direct Reference Functions</td>
+<td><code>std::string::front()</code> and <code>std::string::back()</code></td>
+<td>Returns a reference to the front or back of a string</td>
+<td><a href="http://en.cppreference.com/w/cpp/string/basic_string/front">
+std::basic_string::front</a> and
+<a href="http://en.cppreference.com/w/cpp/string/basic_string/back">
+std::basic_string::back</a></td>
+<td><a href="https://groups.google.com/a/chromium.org/forum/#!topic/cxx/DRJuROAYCV4">Discussion thread</a></td>
+</tr>
+
+<tr>
 <td>Type Traits</td>
 <td>All C++11 features in <code>&lt;type_traits&gt;</code> except for aligned storage (see separate item), e.g.:<br/>
 <code>integral_constant</code><br/>
@@ -985,17 +996,6 @@ std:quick_exit</a></td>
 </tr>
 
 <tr>
-<td>String Direct Reference Functions</td>
-<td><code>std::string::front()</code> and <code>std::string::back()</code></td>
-<td>Returns a reference to the front or back of a string</td>
-<td><a href="http://en.cppreference.com/w/cpp/string/basic_string/front">
-std::basic_string::front</a> and
-<a href="http://en.cppreference.com/w/cpp/string/basic_string/back">
-std::basic_string::back</a></td>
-<td></td>
-</tr>
-
-<tr>
 <td>String to Number Functions</td>
 <td><code>std::stoi()</code>, <code>std::stol()</code>,
 <code>std::stoul()</code>, <code>std::stoll</code>, <code>std::stoull()</code>,
diff --git a/ui/gfx/text_elider.cc b/ui/gfx/text_elider.cc
index 65e24e8..e8993d7 100644
--- a/ui/gfx/text_elider.cc
+++ b/ui/gfx/text_elider.cc
@@ -570,7 +570,7 @@ void RectangleText::AddString(const base::string16& input) {
       // The BREAK_NEWLINE iterator will keep the trailing newline character,
       // except in the case of the last line, which may not have one.  Remove
       // the newline character, if it exists.
-      last_line_ended_in_lf_ = !line.empty() && line[line.length() - 1] == '\n';
+      last_line_ended_in_lf_ = !line.empty() && line.back() == '\n';
       if (last_line_ended_in_lf_)
         line.resize(line.length() - 1);
       AddLine(line);
diff --git a/ui/shell_dialogs/select_file_dialog_win.cc b/ui/shell_dialogs/select_file_dialog_win.cc
index fd48e1f..cbccd3a 100644
--- a/ui/shell_dialogs/select_file_dialog_win.cc
+++ b/ui/shell_dialogs/select_file_dialog_win.cc
@@ -684,7 +684,7 @@ std::wstring AppendExtensionIfNeeded(
   if (!(filter_selected.empty() || filter_selected == L"*.*") &&
       !base::win::RegKey(HKEY_CLASSES_ROOT, key.c_str(), KEY_READ).Valid() &&
       file_extension != suggested_ext) {
-    if (return_value[return_value.length() - 1] != L'.')
+    if (return_value.back() != L'.')
       return_value.append(L".");
     return_value.append(suggested_ext);
   }