[Autofill/Autocomplete Feature] Substring matching instead of prefix matching.

With present implementation autofill/autocomplete suggestions are matched for
prefix for what user has typed.

This patch brings in suggestions with substring matching (i.e. substring
matching to the beginning of suggestion tokens) instead of prefix matching.
This patch keeps the feature behind a command line switch
--enable-suggestions-with-substring-match.

BUG=77194

Review URL: https://codereview.chromium.org/962673004

Cr-Commit-Position: refs/heads/master@{#338677}

25 files changed, 856 insertions, 72 deletions

diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index fc02045..bcbca66 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -6415,6 +6415,12 @@ Keep your key file in a safe place. You will need it to create new versions of y
       <message name="IDS_PASSWORD_MANAGER_SAVE_PASSWORD_SMART_LOCK_NO_THANKS_BUTTON" desc="Text for the button the user clicks to dismiss save password bubble.">
         No thanks
       </message>
+      <message name="IDS_FLAGS_ENABLE_SUGGESTIONS_WITH_SUB_STRING_MATCH_NAME" desc="Name of the flag to enable substring matching for Autofill suggestions.">
+        Substring matching for Autofill suggestions.
+      </message>
+      <message name="IDS_FLAGS_ENABLE_SUGGESTIONS_WITH_SUB_STRING_MATCH_DESCRIPTION" desc="Description of the flag to enable substring matching for Autofill suggestions.">
+        Match Autofill suggestions based on substrings (token prefixes) rather than just prefixes.
+      </message>
       <message name="IDS_FLAGS_ENABLE_AFFILIATION_BASED_MATCHING_NAME" desc="Name of the flag to enable affiliation based matching, so that credentials stored for an Android application will also be considered matches for, and be filled into corresponding websites (so-called 'affiliated' websites).">
         Enable affiliation based matching in password manager.
       </message>
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 94b1ee1..7a56094 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1138,6 +1138,12 @@ const Experiment kExperiments[] = {
      kOsAndroid | kOsCrOS,
      ENABLE_DISABLE_VALUE_TYPE(switches::kEnableSuggestionsService,
                                switches::kDisableSuggestionsService)},
+    {"enable-suggestions-with-substring-match",
+     IDS_FLAGS_ENABLE_SUGGESTIONS_WITH_SUB_STRING_MATCH_NAME,
+     IDS_FLAGS_ENABLE_SUGGESTIONS_WITH_SUB_STRING_MATCH_DESCRIPTION,
+     kOsAll,
+     SINGLE_VALUE_TYPE(
+         autofill::switches::kEnableSuggestionsWithSubstringMatch)},
     {"enable-supervised-user-managed-bookmarks-folder",
      IDS_FLAGS_ENABLE_SUPERVISED_USER_MANAGED_BOOKMARKS_FOLDER_NAME,
      IDS_FLAGS_ENABLE_SUPERVISED_USER_MANAGED_BOOKMARKS_FOLDER_DESCRIPTION,
diff --git a/chrome/browser/chrome_content_browser_client.cc b/chrome/browser/chrome_content_browser_client.cc
index 1ea6058..e00b5e1 100644
--- a/chrome/browser/chrome_content_browser_client.cc
+++ b/chrome/browser/chrome_content_browser_client.cc
@@ -1409,6 +1409,7 @@ void ChromeContentBrowserClient::AppendExtraCommandLineSwitches(
       autofill::switches::kEnableFillOnAccountSelectNoHighlighting,
       autofill::switches::kEnablePasswordGeneration,
       autofill::switches::kEnableSingleClickAutofill,
+      autofill::switches::kEnableSuggestionsWithSubstringMatch,
       autofill::switches::kIgnoreAutocompleteOffForAutofill,
       autofill::switches::kLocalHeuristicsOnlyForPasswordGeneration,
 #if defined(ENABLE_EXTENSIONS)
diff --git a/components/autofill.gypi b/components/autofill.gypi
index 99cc85d..4b1abe4 100644
--- a/components/autofill.gypi
+++ b/components/autofill.gypi
@@ -31,6 +31,8 @@
         'autofill/core/common/autofill_regexes.h',
         'autofill/core/common/autofill_switches.cc',
         'autofill/core/common/autofill_switches.h',
+        'autofill/core/common/autofill_util.cc',
+        'autofill/core/common/autofill_util.h',
         'autofill/core/common/form_data.cc',
         'autofill/core/common/form_data.h',
         'autofill/core/common/form_data_predictions.cc',
diff --git a/components/autofill/content/renderer/autofill_agent.cc b/components/autofill/content/renderer/autofill_agent.cc
index 3c81afe..3412281 100644
--- a/components/autofill/content/renderer/autofill_agent.cc
+++ b/components/autofill/content/renderer/autofill_agent.cc
@@ -739,8 +739,7 @@ void AutofillAgent::PreviewFieldWithValue(const base::string16& value,
   was_query_node_autofilled_ = element_.isAutofilled();
   node->setSuggestedValue(value.substr(0, node->maxLength()));
   node->setAutofilled(true);
-  node->setSelectionRange(node->value().length(),
-                          node->suggestedValue().length());
+  PreviewSuggestion(node->suggestedValue(), node->value(), node);
 }
 
 void AutofillAgent::ProcessForms() {
diff --git a/components/autofill/content/renderer/form_autofill_util.cc b/components/autofill/content/renderer/form_autofill_util.cc
index 51a2251..4cf695f 100644
--- a/components/autofill/content/renderer/form_autofill_util.cc
+++ b/components/autofill/content/renderer/form_autofill_util.cc
@@ -16,6 +16,7 @@
 #include "components/autofill/core/common/autofill_data_validation.h"
 #include "components/autofill/core/common/autofill_regexes.h"
 #include "components/autofill/core/common/autofill_switches.h"
+#include "components/autofill/core/common/autofill_util.h"
 #include "components/autofill/core/common/form_data.h"
 #include "components/autofill/core/common/form_field_data.h"
 #include "third_party/WebKit/public/platform/WebString.h"
@@ -871,9 +872,7 @@ void PreviewFormField(const FormFieldData& data,
   if (is_initiating_node &&
       (IsTextInput(input_element) || IsTextAreaElement(*field))) {
     // Select the part of the text that the user didn't type.
-    int start = field->value().length();
-    int end = field->suggestedValue().length();
-    field->setSelectionRange(start, end);
+    PreviewSuggestion(field->suggestedValue(), field->value(), field);
   }
 }
 
@@ -1534,4 +1533,19 @@ gfx::RectF GetScaledBoundingBox(float scale, WebElement* element) {
                     bounding_box.height() * scale);
 }
 
+void PreviewSuggestion(const base::string16& suggestion,
+                       const base::string16& user_input,
+                       blink::WebFormControlElement* input_element) {
+  size_t selection_start = user_input.length();
+  if (IsFeatureSubstringMatchEnabled()) {
+    size_t offset =
+        autofill::GetTextSelectionStart(suggestion, user_input, false);
+    // Zero selection start is for password manager, which can show usernames
+    // that do not begin with the user input value.
+    selection_start = (offset == base::string16::npos) ? 0 : offset;
+  }
+
+  input_element->setSelectionRange(selection_start, suggestion.length());
+}
+
 }  // namespace autofill
diff --git a/components/autofill/content/renderer/form_autofill_util.h b/components/autofill/content/renderer/form_autofill_util.h
index 1be05cd..985ea16 100644
--- a/components/autofill/content/renderer/form_autofill_util.h
+++ b/components/autofill/content/renderer/form_autofill_util.h
@@ -176,6 +176,15 @@ bool IsWebElementEmpty(const blink::WebElement& element);
 // Return a gfx::RectF that is the bounding box for |element| scaled by |scale|.
 gfx::RectF GetScaledBoundingBox(float scale, blink::WebElement* element);
 
+// Previews |suggestion| in |input_element| and highlights the suffix of
+// |suggestion| not included in the |input_element| text. |input_element| must
+// not be null. |user_input| should be the text typed by the user into
+// |input_element|. Note that |user_input| cannot be easily derived from
+// |input_element| by calling value(), because of http://crbug.com/507714.
+void PreviewSuggestion(const base::string16& suggestion,
+                       const base::string16& user_input,
+                       blink::WebFormControlElement* input_element);
+
 }  // namespace autofill
 
 #endif  // COMPONENTS_AUTOFILL_CONTENT_RENDERER_FORM_AUTOFILL_UTIL_H_
diff --git a/components/autofill/content/renderer/password_autofill_agent.cc b/components/autofill/content/renderer/password_autofill_agent.cc
index 6b87d60..1c836a1 100644
--- a/components/autofill/content/renderer/password_autofill_agent.cc
+++ b/components/autofill/content/renderer/password_autofill_agent.cc
@@ -18,6 +18,7 @@
 #include "components/autofill/content/renderer/renderer_save_password_progress_logger.h"
 #include "components/autofill/core/common/autofill_constants.h"
 #include "components/autofill/core/common/autofill_switches.h"
+#include "components/autofill/core/common/autofill_util.h"
 #include "components/autofill/core/common/form_field_data.h"
 #include "components/autofill/core/common/password_form.h"
 #include "components/autofill/core/common/password_form_fill_data.h"
@@ -226,7 +227,8 @@ bool DoUsernamesMatch(const base::string16& username1,
                       bool exact_match) {
   if (exact_match)
     return username1 == username2;
-  return base::StartsWith(username1, username2, base::CompareCase::SENSITIVE);
+  return FieldIsSuggestionSubstringStartingOnTokenBoundary(username1, username2,
+                                                           true);
 }
 
 // Returns |true| if the given element is editable. Otherwise, returns |false|.
@@ -408,14 +410,12 @@ bool FillUserNameAndPassword(
   // Input matches the username, fill in required values.
   if (!username_element->isNull() &&
       IsElementAutocompletable(*username_element)) {
+    // TODO(vabr): Why not setSuggestedValue? http://crbug.com/507714
     username_element->setValue(username, true);
     (*nonscript_modified_values)[*username_element] = username;
     username_element->setAutofilled(true);
-
-    if (set_selection) {
-      username_element->setSelectionRange(current_username.length(),
-                                          username.length());
-    }
+    if (set_selection)
+      PreviewSuggestion(username, current_username, username_element);
   } else if (current_username != username) {
     // If the username can't be filled and it doesn't match a saved password
     // as is, don't autofill a password.
@@ -561,7 +561,6 @@ PasswordAutofillAgent::PasswordAutofillAgent(content::RenderFrame* render_frame)
       logging_state_active_(false),
       was_username_autofilled_(false),
       was_password_autofilled_(false),
-      username_selection_start_(0),
       did_stop_loading_(false),
       weak_ptr_factory_(this) {
   Send(new AutofillHostMsg_PasswordAutofillAgentConstructed(routing_id()));
@@ -752,14 +751,14 @@ bool PasswordAutofillAgent::PreviewSuggestion(
     return false;
   }
 
+  if (username_query_prefix_.empty())
+    username_query_prefix_ = username_element.value();
+
   was_username_autofilled_ = username_element.isAutofilled();
-  username_selection_start_ = username_element.selectionStart();
   username_element.setSuggestedValue(username);
   username_element.setAutofilled(true);
-  username_element.setSelectionRange(
-      username_selection_start_,
-      username_element.suggestedValue().length());
-
+  ::autofill::PreviewSuggestion(username_element.suggestedValue(),
+                                username_query_prefix_, &username_element);
   was_password_autofilled_ = password_info->password_field.isAutofilled();
   password_info->password_field.setSuggestedValue(password);
   password_info->password_field.setAutofilled(true);
@@ -1304,6 +1303,7 @@ bool PasswordAutofillAgent::ShowSuggestionPopup(
   Send(new AutofillHostMsg_ShowPasswordSuggestions(
       routing_id(), key_it->second, field.text_direction, username_string,
       options, bounding_box_scaled));
+  username_query_prefix_ = username_string;
   return CanShowSuggestion(fill_data, username_string, show_all);
 }
 
@@ -1339,7 +1339,7 @@ void PasswordAutofillAgent::ClearPreview(
   if (!username->suggestedValue().isEmpty()) {
     username->setSuggestedValue(blink::WebString());
     username->setAutofilled(was_username_autofilled_);
-    username->setSelectionRange(username_selection_start_,
+    username->setSelectionRange(username_query_prefix_.length(),
                                 username->value().length());
   }
   if (!password->suggestedValue().isEmpty()) {
diff --git a/components/autofill/content/renderer/password_autofill_agent.h b/components/autofill/content/renderer/password_autofill_agent.h
index 459f7b6..3461d4c 100644
--- a/components/autofill/content/renderer/password_autofill_agent.h
+++ b/components/autofill/content/renderer/password_autofill_agent.h
@@ -272,9 +272,8 @@ class PasswordAutofillAgent : public content::RenderFrameObserver {
   // True indicates that the password field was autofilled, false otherwise.
   bool was_password_autofilled_;
 
-  // Records original starting point of username element's selection range
-  // before preview.
-  int username_selection_start_;
+  // Records the username typed before suggestions preview.
+  base::string16 username_query_prefix_;
 
   // True indicates that all frames in a page have been rendered.
   bool did_stop_loading_;
diff --git a/components/autofill/core/browser/autofill_manager_unittest.cc b/components/autofill/core/browser/autofill_manager_unittest.cc
index 8c960b5..6477ace 100644
--- a/components/autofill/core/browser/autofill_manager_unittest.cc
+++ b/components/autofill/core/browser/autofill_manager_unittest.cc
@@ -3120,4 +3120,176 @@ TEST_F(AutofillManagerTest, FillInUpdatedExpirationDate) {
                                       CREDIT_CARD_EXP_4_DIGIT_YEAR));
 }
 
+// Verify that typing "gmail" will match "theking@gmail.com" and
+// "buddy@gmail.com" when substring matching is enabled.
+TEST_F(AutofillManagerTest, DisplaySuggestionsWithMatchingTokens) {
+  // Token matching is currently behind a flag.
+  base::CommandLine::ForCurrentProcess()->AppendSwitch(
+      autofill::switches::kEnableSuggestionsWithSubstringMatch);
+
+  // Set up our form data.
+  FormData form;
+  test::CreateTestAddressFormData(&form);
+  std::vector<FormData> forms(1, form);
+  FormsSeen(forms);
+
+  FormFieldData field;
+  test::CreateTestFormField("Email", "email", "gmail", "email", &field);
+  GetAutofillSuggestions(form, field);
+  AutocompleteSuggestionsReturned(std::vector<base::string16>());
+
+  external_delegate_->CheckSuggestions(
+      kDefaultPageID,
+      Suggestion("theking@gmail.com", "3734 Elvis Presley Blvd.", "", 1),
+      Suggestion("buddy@gmail.com", "123 Apple St.", "", 2));
+}
+
+// Verify that typing "apple" will match "123 Apple St." when substring matching
+// is enabled.
+TEST_F(AutofillManagerTest, DisplaySuggestionsWithMatchingTokens_CaseIgnored) {
+  // Token matching is currently behind a flag.
+  base::CommandLine::ForCurrentProcess()->AppendSwitch(
+      autofill::switches::kEnableSuggestionsWithSubstringMatch);
+
+  // Set up our form data.
+  FormData form;
+  test::CreateTestAddressFormData(&form);
+  std::vector<FormData> forms(1, form);
+  FormsSeen(forms);
+
+  FormFieldData field;
+  test::CreateTestFormField("Address Line 2", "addr2", "apple", "text", &field);
+  GetAutofillSuggestions(form, field);
+  AutocompleteSuggestionsReturned(std::vector<base::string16>());
+
+  external_delegate_->CheckSuggestions(
+      kDefaultPageID,
+      Suggestion("123 Apple St., unit 6", "123 Apple St.", "", 1));
+}
+
+// Verify that typing "mail" will not match any of the "@gmail.com" email
+// addresses when substring matching is enabled.
+TEST_F(AutofillManagerTest, NoSuggestionForNonPrefixTokenMatch) {
+  // Token matching is currently behind a flag.
+  base::CommandLine::ForCurrentProcess()->AppendSwitch(
+      autofill::switches::kEnableSuggestionsWithSubstringMatch);
+
+  // Set up our form data.
+  FormData form;
+  test::CreateTestAddressFormData(&form);
+  std::vector<FormData> forms(1, form);
+  FormsSeen(forms);
+
+  FormFieldData field;
+  test::CreateTestFormField("Email", "email", "mail", "email", &field);
+  GetAutofillSuggestions(form, field);
+  EXPECT_FALSE(external_delegate_->on_suggestions_returned_seen());
+}
+
+// Verify that typing "pres" will match "Elvis Presley" when substring matching
+// is enabled.
+TEST_F(AutofillManagerTest, DisplayCreditCardSuggestionsWithMatchingTokens) {
+  // Token matching is currently behind a flag.
+  base::CommandLine::ForCurrentProcess()->AppendSwitch(
+      autofill::switches::kEnableSuggestionsWithSubstringMatch);
+
+  // Set up our form data.
+  FormData form;
+  CreateTestCreditCardFormData(&form, true, false);
+  std::vector<FormData> forms(1, form);
+  FormsSeen(forms);
+
+  FormFieldData field;
+  test::CreateTestFormField("Name on Card", "nameoncard", "pres", "text",
+                            &field);
+  GetAutofillSuggestions(form, field);
+
+  // No suggestions provided, so send an empty vector as the results.
+  // This triggers the combined message send.
+  AutocompleteSuggestionsReturned(std::vector<base::string16>());
+
+#if defined(OS_ANDROID)
+  static const char* kVisaSuggestion =
+      "Visa\xC2\xA0\xE2\x8B\xAF"
+      "3456";
+#else
+  static const char* kVisaSuggestion = "*3456";
+#endif
+
+  external_delegate_->CheckSuggestions(
+      kDefaultPageID, Suggestion("Elvis Presley", kVisaSuggestion, kVisaCard,
+                                 autofill_manager_->GetPackedCreditCardID(4)));
+}
+
+// Verify that typing "lvis" will not match any of the credit card name when
+// substring matching is enabled.
+TEST_F(AutofillManagerTest, NoCreditCardSuggestionsForNonPrefixTokenMatch) {
+  // Token matching is currently behind a flag.
+  base::CommandLine::ForCurrentProcess()->AppendSwitch(
+      autofill::switches::kEnableSuggestionsWithSubstringMatch);
+
+  // Set up our form data.
+  FormData form;
+  CreateTestCreditCardFormData(&form, true, false);
+  std::vector<FormData> forms(1, form);
+  FormsSeen(forms);
+
+  FormFieldData field;
+  test::CreateTestFormField("Name on Card", "nameoncard", "lvis", "text",
+                            &field);
+  GetAutofillSuggestions(form, field);
+  EXPECT_FALSE(external_delegate_->on_suggestions_returned_seen());
+}
+
+// Verify that typing "S" into the middle name field will match and order middle
+// names "Shawn Smith" followed by "Adam Smith" i.e. prefix matched followed by
+// substring matched.
+TEST_F(AutofillManagerTest,
+       DisplaySuggestionsWithPrefixesPrecedeSubstringMatched) {
+  // Token matching is currently behind a flag.
+  base::CommandLine::ForCurrentProcess()->AppendSwitch(
+      autofill::switches::kEnableSuggestionsWithSubstringMatch);
+
+  // Set up our form data.
+  FormData form;
+  test::CreateTestAddressFormData(&form);
+  std::vector<FormData> forms(1, form);
+  FormsSeen(forms);
+
+  AutofillProfile* profile1 = new AutofillProfile;
+  profile1->set_guid("00000000-0000-0000-0000-000000000103");
+  profile1->SetInfo(AutofillType(NAME_FIRST), ASCIIToUTF16("Robin"), "en-US");
+  profile1->SetInfo(AutofillType(NAME_MIDDLE), ASCIIToUTF16("Adam Smith"),
+                    "en-US");
+  profile1->SetInfo(AutofillType(NAME_LAST), ASCIIToUTF16("Grimes"), "en-US");
+  profile1->SetInfo(AutofillType(ADDRESS_HOME_LINE1),
+                    ASCIIToUTF16("1234 Smith Blvd."), "en-US");
+  autofill_manager_->AddProfile(profile1);
+
+  AutofillProfile* profile2 = new AutofillProfile;
+  profile2->set_guid("00000000-0000-0000-0000-000000000124");
+  profile2->SetInfo(AutofillType(NAME_FIRST), ASCIIToUTF16("Carl"), "en-US");
+  profile2->SetInfo(AutofillType(NAME_MIDDLE), ASCIIToUTF16("Shawn Smith"),
+                    "en-US");
+  profile2->SetInfo(AutofillType(NAME_LAST), ASCIIToUTF16("Grimes"), "en-US");
+  profile2->SetInfo(AutofillType(ADDRESS_HOME_LINE1),
+                    ASCIIToUTF16("1234 Smith Blvd."), "en-US");
+  autofill_manager_->AddProfile(profile2);
+
+  FormFieldData field;
+  test::CreateTestFormField("Middle Name", "middlename", "S", "text", &field);
+  GetAutofillSuggestions(form, field);
+
+  // No suggestions provided, so send an empty vector as the results.
+  // This triggers the combined message send.
+  AutocompleteSuggestionsReturned(std::vector<base::string16>());
+
+  external_delegate_->CheckSuggestions(
+      kDefaultPageID,
+      Suggestion("Shawn Smith", "1234 Smith Blvd., Robin Adam Smith Grimes", "",
+                 1),
+      Suggestion("Adam Smith", "1234 Smith Blvd., Carl Shawn Smith Grimes", "",
+                 2));
+}
+
 }  // namespace autofill
diff --git a/components/autofill/core/browser/personal_data_manager.cc b/components/autofill/core/browser/personal_data_manager.cc
index 980448b..da9a59f 100644
--- a/components/autofill/core/browser/personal_data_manager.cc
+++ b/components/autofill/core/browser/personal_data_manager.cc
@@ -31,6 +31,7 @@
 #include "components/autofill/core/browser/validation.h"
 #include "components/autofill/core/common/autofill_pref_names.h"
 #include "components/autofill/core/common/autofill_switches.h"
+#include "components/autofill/core/common/autofill_util.h"
 #include "components/signin/core/browser/account_tracker_service.h"
 #include "components/signin/core/common/signin_pref_names.h"
 #include "third_party/libaddressinput/src/cpp/include/libaddressinput/address_data.h"
@@ -796,15 +797,28 @@ std::vector<Suggestion> PersonalDataManager::GetProfileSuggestions(
       continue;
     base::string16 value_canon =
         AutofillProfile::CanonicalizeProfileString(value);
-    if (base::StartsWith(value_canon, field_contents_canon,
-                         base::CompareCase::SENSITIVE)) {
-      // Prefix match, add suggestion.
+    bool prefix_matched_suggestion = base::StartsWith(
+        value_canon, field_contents_canon, base::CompareCase::SENSITIVE);
+    if (prefix_matched_suggestion ||
+        FieldIsSuggestionSubstringStartingOnTokenBoundary(value, field_contents,
+                                                          false)) {
       matched_profiles.push_back(profile);
       suggestions.push_back(Suggestion(value));
       suggestions.back().backend_id = profile->guid();
+      suggestions.back().match = prefix_matched_suggestion
+                                     ? Suggestion::PREFIX_MATCH
+                                     : Suggestion::SUBSTRING_MATCH;
     }
   }
 
+  // Prefix matches should precede other token matches.
+  if (IsFeatureSubstringMatchEnabled()) {
+    std::stable_sort(suggestions.begin(), suggestions.end(),
+                     [](const Suggestion& a, const Suggestion& b) {
+                       return a.match < b.match;
+                     });
+  }
+
   // Don't show two suggestions if one is a subset of the other.
   std::vector<AutofillProfile*> unique_matched_profiles;
   std::vector<Suggestion> unique_suggestions;
@@ -856,6 +870,7 @@ std::vector<Suggestion> PersonalDataManager::GetCreditCardSuggestions(
     return std::vector<Suggestion>();
 
   std::list<const CreditCard*> cards_to_suggest;
+  std::list<const CreditCard*> substring_matched_cards;
   base::string16 field_contents_lower = base::i18n::ToLower(field_contents);
   for (const CreditCard* credit_card : GetCreditCards()) {
     // The value of the stored data for this field type in the |credit_card|.
@@ -878,12 +893,24 @@ std::vector<Suggestion> PersonalDataManager::GetCreditCardSuggestions(
            field_contents.size() >= 6)) {
         continue;
       }
-    } else if (!base::StartsWith(creditcard_field_lower, field_contents_lower,
-                                 base::CompareCase::SENSITIVE)) {
-      continue;
+      cards_to_suggest.push_back(credit_card);
+    } else if (base::StartsWith(creditcard_field_lower, field_contents_lower,
+                                base::CompareCase::SENSITIVE)) {
+      cards_to_suggest.push_back(credit_card);
+    } else if (FieldIsSuggestionSubstringStartingOnTokenBoundary(
+                   creditcard_field_lower, field_contents_lower, true)) {
+      substring_matched_cards.push_back(credit_card);
     }
+  }
 
-    cards_to_suggest.push_back(credit_card);
+  cards_to_suggest.sort(RankByMfu);
+
+  // Prefix matches should precede other token matches.
+  if (IsFeatureSubstringMatchEnabled()) {
+    substring_matched_cards.sort(RankByMfu);
+    cards_to_suggest.insert(cards_to_suggest.end(),
+                            substring_matched_cards.begin(),
+                            substring_matched_cards.end());
   }
 
   // De-dupe card suggestions. Full server cards shadow local cards, and
@@ -911,8 +938,6 @@ std::vector<Suggestion> PersonalDataManager::GetCreditCardSuggestions(
     }
   }
 
-  cards_to_suggest.sort(RankByMfu);
-
   std::vector<Suggestion> suggestions;
   for (const CreditCard* credit_card : cards_to_suggest) {
     // Make a new suggestion.
diff --git a/components/autofill/core/browser/suggestion.cc b/components/autofill/core/browser/suggestion.cc
index c46d302..c5b150e 100644
--- a/components/autofill/core/browser/suggestion.cc
+++ b/components/autofill/core/browser/suggestion.cc
@@ -11,7 +11,8 @@
 namespace autofill {
 
 Suggestion::Suggestion()
-    : frontend_id(0) {
+    : frontend_id(0),
+      match(PREFIX_MATCH) {
 }
 
 Suggestion::Suggestion(const Suggestion& other)
@@ -19,12 +20,14 @@ Suggestion::Suggestion(const Suggestion& other)
       frontend_id(other.frontend_id),
       value(other.value),
       label(other.label),
-      icon(other.icon) {
+      icon(other.icon),
+      match(other.match) {
 }
 
 Suggestion::Suggestion(const base::string16& v)
     : frontend_id(0),
-      value(v) {
+      value(v),
+      match(PREFIX_MATCH) {
 }
 
 Suggestion::Suggestion(const std::string& v,
@@ -34,7 +37,8 @@ Suggestion::Suggestion(const std::string& v,
     : frontend_id(fid),
       value(base::UTF8ToUTF16(v)),
       label(base::UTF8ToUTF16(l)),
-      icon(base::UTF8ToUTF16(i)) {
+      icon(base::UTF8ToUTF16(i)),
+      match(PREFIX_MATCH) {
 }
 
 Suggestion::~Suggestion() {
diff --git a/components/autofill/core/browser/suggestion.h b/components/autofill/core/browser/suggestion.h
index 6077185..ebf1607 100644
--- a/components/autofill/core/browser/suggestion.h
+++ b/components/autofill/core/browser/suggestion.h
@@ -17,6 +17,11 @@ class CreditCard;
 
 struct Suggestion {
  public:
+  enum MatchMode {
+    PREFIX_MATCH,    // for prefix matched suggestions;
+    SUBSTRING_MATCH  // for substring matched suggestions;
+  };
+
   Suggestion();
 
   // Copy constructor for STL containers.
@@ -46,6 +51,7 @@ struct Suggestion {
   base::string16 value;
   base::string16 label;
   base::string16 icon;
+  MatchMode match;
 };
 
 }  // namespace autofill
diff --git a/components/autofill/core/browser/webdata/autofill_table.cc b/components/autofill/core/browser/webdata/autofill_table.cc
index c337f60..2ee8455 100644
--- a/components/autofill/core/browser/webdata/autofill_table.cc
+++ b/components/autofill/core/browser/webdata/autofill_table.cc
@@ -18,6 +18,7 @@
 #include "base/logging.h"
 #include "base/numerics/safe_conversions.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/time/time.h"
 #include "components/autofill/core/browser/autofill_country.h"
@@ -28,6 +29,7 @@
 #include "components/autofill/core/browser/webdata/autofill_change.h"
 #include "components/autofill/core/browser/webdata/autofill_entry.h"
 #include "components/autofill/core/common/autofill_switches.h"
+#include "components/autofill/core/common/autofill_util.h"
 #include "components/autofill/core/common/form_field_data.h"
 #include "components/os_crypt/os_crypt.h"
 #include "components/webdata/common/web_database.h"
@@ -368,6 +370,28 @@ CreditCard::ServerStatus ServerStatusStringToEnum(const std::string& status) {
   return CreditCard::OK;
 }
 
+// Returns |s| with |escaper| in front of each of occurrence of a character from
+// |special_chars|. Any occurrence of |escaper| in |s| is doubled. For example,
+// Substitute("hello_world!", "_%", '!'') returns "hello!_world!!".
+base::string16 Substitute(const base::string16& s,
+                          const base::string16& special_chars,
+                          const base::char16& escaper) {
+  // Prepend |escaper| to the list of |special_chars|.
+  base::string16 escape_wildcards(special_chars);
+  escape_wildcards.insert(escape_wildcards.begin(), escaper);
+
+  // Prepend the |escaper| just before |special_chars| in |s|.
+  base::string16 result(s);
+  for (base::char16 c : escape_wildcards) {
+    for (size_t pos = 0; (pos = result.find(c, pos)) != base::string16::npos;
+         pos += 2) {
+      result.insert(result.begin() + pos, escaper);
+    }
+  }
+
+  return result;
+}
+
 }  // namespace
 
 // The maximum length allowed for form data.
@@ -456,9 +480,10 @@ bool AutofillTable::GetFormValuesForElementName(
     std::vector<base::string16>* values,
     int limit) {
   DCHECK(values);
-  sql::Statement s;
+  bool succeeded = false;
 
   if (prefix.empty()) {
+    sql::Statement s;
     s.Assign(db_->GetUniqueStatement(
         "SELECT value FROM autofill "
         "WHERE name = ? "
@@ -466,28 +491,62 @@ bool AutofillTable::GetFormValuesForElementName(
         "LIMIT ?"));
     s.BindString16(0, name);
     s.BindInt(1, limit);
+
+    values->clear();
+    while (s.Step())
+      values->push_back(s.ColumnString16(0));
+
+    succeeded = s.Succeeded();
   } else {
     base::string16 prefix_lower = base::i18n::ToLower(prefix);
     base::string16 next_prefix = prefix_lower;
     next_prefix[next_prefix.length() - 1]++;
 
-    s.Assign(db_->GetUniqueStatement(
+    sql::Statement s1;
+    s1.Assign(db_->GetUniqueStatement(
         "SELECT value FROM autofill "
         "WHERE name = ? AND "
         "value_lower >= ? AND "
         "value_lower < ? "
         "ORDER BY count DESC "
         "LIMIT ?"));
-    s.BindString16(0, name);
-    s.BindString16(1, prefix_lower);
-    s.BindString16(2, next_prefix);
-    s.BindInt(3, limit);
+    s1.BindString16(0, name);
+    s1.BindString16(1, prefix_lower);
+    s1.BindString16(2, next_prefix);
+    s1.BindInt(3, limit);
+
+    values->clear();
+    while (s1.Step())
+      values->push_back(s1.ColumnString16(0));
+
+    succeeded = s1.Succeeded();
+
+    if (IsFeatureSubstringMatchEnabled()) {
+      sql::Statement s2;
+      s2.Assign(db_->GetUniqueStatement(
+          "SELECT value FROM autofill "
+          "WHERE name = ? AND ("
+          " value LIKE '% ' || :prefix || '%' ESCAPE '!' OR "
+          " value LIKE '%.' || :prefix || '%' ESCAPE '!' OR "
+          " value LIKE '%,' || :prefix || '%' ESCAPE '!' OR "
+          " value LIKE '%-' || :prefix || '%' ESCAPE '!' OR "
+          " value LIKE '%@' || :prefix || '%' ESCAPE '!' OR "
+          " value LIKE '%!_' || :prefix || '%' ESCAPE '!' ) "
+          "ORDER BY count DESC "
+          "LIMIT ?"));
+
+      s2.BindString16(0, name);
+      // escaper as L'!' -> 0x21.
+      s2.BindString16(1, Substitute(prefix_lower, ASCIIToUTF16("_%"), 0x21));
+      s2.BindInt(2, limit);
+      while (s2.Step())
+        values->push_back(s2.ColumnString16(0));
+
+      succeeded &= s2.Succeeded();
+    }
   }
 
-  values->clear();
-  while (s.Step())
-    values->push_back(s.ColumnString16(0));
-  return s.Succeeded();
+  return succeeded;
 }
 
 bool AutofillTable::HasFormElements() {
diff --git a/components/autofill/core/browser/webdata/autofill_table_unittest.cc b/components/autofill/core/browser/webdata/autofill_table_unittest.cc
index f3cf200..af71b6c 100644
--- a/components/autofill/core/browser/webdata/autofill_table_unittest.cc
+++ b/components/autofill/core/browser/webdata/autofill_table_unittest.cc
@@ -5,6 +5,7 @@
 #include <utility>
 #include <vector>
 
+#include "base/command_line.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/guid.h"
@@ -21,6 +22,8 @@
 #include "components/autofill/core/browser/webdata/autofill_change.h"
 #include "components/autofill/core/browser/webdata/autofill_entry.h"
 #include "components/autofill/core/browser/webdata/autofill_table.h"
+#include "components/autofill/core/common/autofill_switches.h"
+#include "components/autofill/core/common/autofill_util.h"
 #include "components/autofill/core/common/form_field_data.h"
 #include "components/os_crypt/os_crypt.h"
 #include "components/webdata/common/web_database.h"
@@ -1856,4 +1859,60 @@ TEST_F(AutofillTableTest, DeleteUnmaskedCard) {
   outputs.clear();
 }
 
+TEST_F(AutofillTableTest, GetFormValuesForElementName_SubstringMatchEnabled) {
+  // Token matching is currently behind a flag.
+  base::CommandLine::ForCurrentProcess()->AppendSwitch(
+      autofill::switches::kEnableSuggestionsWithSubstringMatch);
+
+  const size_t kMaxCount = 2;
+  const struct {
+    const char* const field_suggestion[kMaxCount];
+    const char* const field_contents;
+    size_t expected_suggestion_count;
+    const char* const expected_suggestion[kMaxCount];
+  } kTestCases[] = {
+      {{"user.test", "test_user"}, "TEST",   2, {"test_user", "user.test"}},
+      {{"user test", "test-user"}, "user",   2, {"user test", "test-user"}},
+      {{"user test", "test-rest"}, "user",   1, {"user test", nullptr}},
+      {{"user@test", "test_user"}, "user@t", 1, {"user@test", nullptr}},
+      {{"user.test", "test_user"}, "er.tes", 0, {nullptr,     nullptr}},
+      {{"user test", "test_user"}, "_ser",   0, {nullptr,     nullptr}},
+      {{"user.test", "test_user"}, "%ser",   0, {nullptr,     nullptr}},
+      {{"user.test", "test_user"},
+       "; DROP TABLE autofill;",
+       0,
+       {nullptr, nullptr}},
+  };
+
+  for (size_t i = 0; i < arraysize(kTestCases); ++i) {
+    SCOPED_TRACE(testing::Message()
+                 << "suggestion = " << kTestCases[i].field_suggestion[0]
+                 << ", contents = " << kTestCases[i].field_contents);
+
+    Time t1 = Time::Now();
+
+    // Simulate the submission of a handful of entries in a field called "Name".
+    AutofillChangeList changes;
+    FormFieldData field;
+    for (size_t k = 0; k < kMaxCount; ++k) {
+      field.name = ASCIIToUTF16("Name");
+      field.value = ASCIIToUTF16(kTestCases[i].field_suggestion[k]);
+      table_->AddFormFieldValue(field, &changes);
+    }
+
+    std::vector<base::string16> v;
+    table_->GetFormValuesForElementName(
+        ASCIIToUTF16("Name"), ASCIIToUTF16(kTestCases[i].field_contents), &v,
+        6);
+
+    EXPECT_EQ(kTestCases[i].expected_suggestion_count, v.size());
+    for (size_t j = 0; j < kTestCases[i].expected_suggestion_count; ++j) {
+      EXPECT_EQ(ASCIIToUTF16(kTestCases[i].expected_suggestion[j]), v[j]);
+    }
+
+    changes.clear();
+    table_->RemoveFormElementsAddedBetween(t1, Time(), &changes);
+  }
+}
+
 }  // namespace autofill
diff --git a/components/autofill/core/common/BUILD.gn b/components/autofill/core/common/BUILD.gn
index ed9d589..9a53fe2 100644
--- a/components/autofill/core/common/BUILD.gn
+++ b/components/autofill/core/common/BUILD.gn
@@ -16,6 +16,8 @@ static_library("common") {
     "autofill_regexes.h",
     "autofill_switches.cc",
     "autofill_switches.h",
+    "autofill_util.cc",
+    "autofill_util.h",
     "form_data.cc",
     "form_data.h",
     "form_data_predictions.cc",
@@ -55,6 +57,7 @@ source_set("unit_tests") {
   testonly = true
   sources = [
     "autofill_regexes_unittest.cc",
+    "autofill_util_unittest.cc",
     "form_data_unittest.cc",
     "form_field_data_unittest.cc",
     "password_form_fill_data_unittest.cc",
diff --git a/components/autofill/core/common/autofill_switches.cc b/components/autofill/core/common/autofill_switches.cc
index 675475a..0178335 100644
--- a/components/autofill/core/common/autofill_switches.cc
+++ b/components/autofill/core/common/autofill_switches.cc
@@ -63,6 +63,10 @@ const char kEnablePasswordGeneration[]      = "enable-password-generation";
 // Enables/disables suggestions without typing anything (on first click).
 const char kEnableSingleClickAutofill[]     = "enable-single-click-autofill";
 
+// Enables suggestions with substring matching instead of prefix matching.
+const char kEnableSuggestionsWithSubstringMatch[] =
+    "enable-suggestions-with-substring-match";
+
 // Enables syncing usage counts and last use dates of Wallet addresses and
 // cards.
 const char kEnableWalletMetadataSync[]      = "enable-wallet-metadata-sync";
diff --git a/components/autofill/core/common/autofill_switches.h b/components/autofill/core/common/autofill_switches.h
index 2c6ee91..0ce9bf7 100644
--- a/components/autofill/core/common/autofill_switches.h
+++ b/components/autofill/core/common/autofill_switches.h
@@ -24,6 +24,7 @@ extern const char kEnableFullFormAutofillIOS[];
 extern const char kEnableOfferStoreUnmaskedWalletCards[];
 extern const char kEnablePasswordGeneration[];
 extern const char kEnableSingleClickAutofill[];
+extern const char kEnableSuggestionsWithSubstringMatch[];
 extern const char kEnableWalletMetadataSync[];
 extern const char kIgnoreAutocompleteOffForAutofill[];
 extern const char kLocalHeuristicsOnlyForPasswordGeneration[];
diff --git a/components/autofill/core/common/autofill_util.cc b/components/autofill/core/common/autofill_util.cc
new file mode 100644
index 0000000..a313fc9
--- /dev/null
+++ b/components/autofill/core/common/autofill_util.cc
@@ -0,0 +1,85 @@
+// Copyright 2015 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 "components/autofill/core/common/autofill_util.h"
+
+#include <algorithm>
+#include <vector>
+
+#include "base/command_line.h"
+#include "base/i18n/case_conversion.h"
+#include "base/strings/string_piece.h"
+#include "base/strings/string_split.h"
+#include "base/strings/string_util.h"
+#include "base/strings/utf_string_conversions.h"
+#include "components/autofill/core/common/autofill_switches.h"
+
+namespace autofill {
+
+namespace {
+
+const char kSplitCharacters[] = " .,-_@";
+
+template <typename Char>
+struct Compare : base::CaseInsensitiveCompareASCII<Char> {
+  explicit Compare(bool case_sensitive) : case_sensitive_(case_sensitive) {}
+  bool operator()(Char x, Char y) const {
+    return case_sensitive_ ? (x == y)
+                           : base::CaseInsensitiveCompareASCII<Char>::
+                             operator()(x, y);
+  }
+
+ private:
+  bool case_sensitive_;
+};
+
+}  // namespace
+
+bool IsFeatureSubstringMatchEnabled() {
+  return base::CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kEnableSuggestionsWithSubstringMatch);
+}
+
+bool FieldIsSuggestionSubstringStartingOnTokenBoundary(
+    const base::string16& suggestion,
+    const base::string16& field_contents,
+    bool case_sensitive) {
+  if (!IsFeatureSubstringMatchEnabled()) {
+    return base::StartsWith(suggestion, field_contents,
+                            case_sensitive
+                                ? base::CompareCase::SENSITIVE
+                                : base::CompareCase::INSENSITIVE_ASCII);
+  }
+
+  return suggestion.length() >= field_contents.length() &&
+         GetTextSelectionStart(suggestion, field_contents, case_sensitive) !=
+             base::string16::npos;
+}
+
+size_t GetTextSelectionStart(const base::string16& suggestion,
+                             const base::string16& field_contents,
+                             bool case_sensitive) {
+  const base::string16 kSplitChars = base::ASCIIToUTF16(kSplitCharacters);
+
+  // Loop until we find either the |field_contents| is a prefix of |suggestion|
+  // or character right before the match is one of the splitting characters.
+  for (base::string16::const_iterator it = suggestion.begin();
+       (it = std::search(
+            it, suggestion.end(), field_contents.begin(), field_contents.end(),
+            Compare<base::string16::value_type>(case_sensitive))) !=
+           suggestion.end();
+       ++it) {
+    if (it == suggestion.begin() ||
+        kSplitChars.find(*(it - 1)) != std::string::npos) {
+      // Returns the character position right after the |field_contents| within
+      // |suggestion| text as a caret position for text selection.
+      return it - suggestion.begin() + field_contents.size();
+    }
+  }
+
+  // Unable to find the |field_contents| in |suggestion| text.
+  return base::string16::npos;
+}
+
+}  // namespace autofill
diff --git a/components/autofill/core/common/autofill_util.h b/components/autofill/core/common/autofill_util.h
new file mode 100644
index 0000000..18c487e
--- /dev/null
+++ b/components/autofill/core/common/autofill_util.h
@@ -0,0 +1,38 @@
+// Copyright 2015 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.
+
+#ifndef COMPONENTS_AUTOFILL_CORE_COMMON_AUTOFILL_UTIL_H_
+#define COMPONENTS_AUTOFILL_CORE_COMMON_AUTOFILL_UTIL_H_
+
+#include "base/strings/string16.h"
+
+namespace autofill {
+
+// Returns true when command line switch |kEnableSuggestionsWithSubstringMatch|
+// is on.
+bool IsFeatureSubstringMatchEnabled();
+
+// A token is a sequences of contiguous characters separated by any of the
+// characters that are part of delimiter set {' ', '.', ',', '-', '_', '@'}.
+
+// Returns true if the |field_contents| is a substring of the |suggestion|
+// starting at token boundaries. |field_contents| can span multiple |suggestion|
+// tokens.
+bool FieldIsSuggestionSubstringStartingOnTokenBoundary(
+    const base::string16& suggestion,
+    const base::string16& field_contents,
+    bool case_sensitive);
+
+// Finds the first occurrence of a searched substring |field_contents| within
+// the string |suggestion| starting at token boundaries and returns the index to
+// the end of the located substring, or base::string16::npos if the substring is
+// not found. "preview-on-hover" feature is one such use case where the
+// substring |field_contents| may not be found within the string |suggestion|.
+size_t GetTextSelectionStart(const base::string16& suggestion,
+                             const base::string16& field_contents,
+                             bool case_sensitive);
+
+}  // namespace autofill
+
+#endif  // COMPONENTS_AUTOFILL_CORE_COMMON_AUTOFILL_UTIL_H_
diff --git a/components/autofill/core/common/autofill_util_unittest.cc b/components/autofill/core/common/autofill_util_unittest.cc
new file mode 100644
index 0000000..fc7bf61
--- /dev/null
+++ b/components/autofill/core/common/autofill_util_unittest.cc
@@ -0,0 +1,99 @@
+// Copyright 2015 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 "components/autofill/core/common/autofill_util.h"
+
+#include "base/command_line.h"
+#include "base/strings/utf_string_conversions.h"
+#include "components/autofill/core/common/autofill_switches.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace autofill {
+
+// Tests for FieldIsSuggestionSubstringStartingOnTokenBoundary().
+TEST(AutofillUtilTest, FieldIsSuggestionSubstringStartingOnTokenBoundary) {
+  // FieldIsSuggestionSubstringStartingOnTokenBoundary should not work yet
+  // without a flag.
+  EXPECT_FALSE(FieldIsSuggestionSubstringStartingOnTokenBoundary(
+      base::ASCIIToUTF16("ab@cd.b"), base::ASCIIToUTF16("b"), false));
+
+  // Token matching is currently behind a flag.
+  base::CommandLine::ForCurrentProcess()->AppendSwitch(
+      autofill::switches::kEnableSuggestionsWithSubstringMatch);
+
+  const struct {
+    const char* const field_suggestion;
+    const char* const field_contents;
+    bool case_sensitive;
+    bool expected_result;
+  } kTestCases[] = {
+      {"ab@cd.b", "a",    false, true},
+      {"ab@cd.b", "b",    false, true},
+      {"ab@cd.b", "Ab",   false, true},
+      {"ab@cd.b", "Ab",   true,  false},
+      {"ab@cd.b", "cd",   true,  true},
+      {"ab@cd.b", "d",    false, false},
+      {"ab@cd.b", "b@",   true,  false},
+      {"ab@cd.b", "ab",   false, true},
+      {"ab@cd.b", "cd.b", true,  true},
+      {"ab@cd.b", "b@cd", false, false},
+      {"ab@cd.b", "ab@c", false, true},
+      {"ba.a.ab", "a.a",  false, true},
+      {"",        "ab",   false, false},
+      {"",        "ab",   true,  false},
+      {"ab",      "",     false, true},
+      {"ab",      "",     true,  true},
+  };
+
+  for (size_t i = 0; i < arraysize(kTestCases); ++i) {
+    SCOPED_TRACE(testing::Message()
+                 << "suggestion = " << kTestCases[i].field_suggestion
+                 << ", contents = " << kTestCases[i].field_contents
+                 << ", case_sensitive = " << kTestCases[i].case_sensitive);
+
+    EXPECT_EQ(kTestCases[i].expected_result,
+              FieldIsSuggestionSubstringStartingOnTokenBoundary(
+                  base::ASCIIToUTF16(kTestCases[i].field_suggestion),
+                  base::ASCIIToUTF16(kTestCases[i].field_contents),
+                  kTestCases[i].case_sensitive));
+  }
+}
+
+// Tests for GetTextSelectionStart().
+TEST(AutofillUtilTest, GetTextSelectionStart) {
+  const size_t kInvalid = base::string16::npos;
+  const struct {
+    const char* const field_suggestion;
+    const char* const field_contents;
+    bool case_sensitive;
+    size_t expected_start;
+  } kTestCases[] = {
+      {"ab@cd.b",              "a",       false, 1},
+      {"ab@cd.b",              "A",       true,  kInvalid},
+      {"ab@cd.b",              "Ab",      false, 2},
+      {"ab@cd.b",              "Ab",      true,  kInvalid},
+      {"ab@cd.b",              "cd",      false, 5},
+      {"ab@cd.b",              "ab@c",    false, 4},
+      {"ab@cd.b",              "cd.b",    false, 7},
+      {"ab@cd.b",              "b@cd",    false, kInvalid},
+      {"ab@cd.b",              "b",       false, 7},
+      {"ba.a.ab",              "a.a",     false, 6},
+      {"texample@example.com", "example", false, 16},
+  };
+
+  for (size_t i = 0; i < arraysize(kTestCases); ++i) {
+    SCOPED_TRACE(testing::Message()
+                 << "suggestion = " << kTestCases[i].field_suggestion
+                 << ", contents = " << kTestCases[i].field_contents
+                 << ", case_sensitive = " << kTestCases[i].case_sensitive);
+
+    EXPECT_EQ(kTestCases[i].expected_start,
+              GetTextSelectionStart(
+                  base::ASCIIToUTF16(kTestCases[i].field_suggestion),
+                  base::ASCIIToUTF16(kTestCases[i].field_contents),
+                  kTestCases[i].case_sensitive));
+  }
+}
+
+}  // autofill
diff --git a/components/components_tests.gyp b/components/components_tests.gyp
index 4bf8a14..02c39b3 100644
--- a/components/components_tests.gyp
+++ b/components/components_tests.gyp
@@ -62,6 +62,7 @@
       'autofill/core/browser/webdata/autofill_wallet_metadata_syncable_service_unittest.cc',
       'autofill/core/browser/webdata/web_data_service_unittest.cc',
       'autofill/core/common/autofill_regexes_unittest.cc',
+      'autofill/core/common/autofill_util_unittest.cc',
       'autofill/core/common/form_data_unittest.cc',
       'autofill/core/common/form_field_data_unittest.cc',
       'autofill/core/common/password_form_fill_data_unittest.cc',
diff --git a/components/password_manager/core/browser/password_autofill_manager.cc b/components/password_manager/core/browser/password_autofill_manager.cc
index d0af275..3100bdd 100644
--- a/components/password_manager/core/browser/password_autofill_manager.cc
+++ b/components/password_manager/core/browser/password_autofill_manager.cc
@@ -17,6 +17,7 @@
 #include "components/autofill/core/browser/suggestion.h"
 #include "components/autofill/core/common/autofill_constants.h"
 #include "components/autofill/core/common/autofill_data_validation.h"
+#include "components/autofill/core/common/autofill_util.h"
 #include "components/password_manager/core/browser/affiliation_utils.h"
 #include "components/password_manager/core/browser/password_manager_driver.h"
 #include "components/password_manager/core/browser/password_manager_metrics_util.h"
@@ -60,6 +61,32 @@ base::string16 GetHumanReadableRealm(const std::string& signon_realm) {
   return base::UTF8ToUTF16(signon_realm);
 }
 
+// If |field_suggestion| matches |field_content|, creates a Suggestion out of it
+// and appends to |suggestions|.
+void AppendSuggestionIfMatching(
+    const base::string16& field_suggestion,
+    const base::string16& field_contents,
+    const std::string& signon_realm,
+    bool show_all,
+    std::vector<autofill::Suggestion>* suggestions) {
+  base::string16 lower_suggestion = base::i18n::ToLower(field_suggestion);
+  base::string16 lower_contents = base::i18n::ToLower(field_contents);
+  bool prefix_matched_suggestion =
+      show_all || base::StartsWith(lower_suggestion, lower_contents,
+                                   base::CompareCase::SENSITIVE);
+  if (prefix_matched_suggestion ||
+      autofill::FieldIsSuggestionSubstringStartingOnTokenBoundary(
+          lower_suggestion, lower_contents, true)) {
+    autofill::Suggestion suggestion(ReplaceEmptyUsername(field_suggestion));
+    suggestion.label = GetHumanReadableRealm(signon_realm);
+    suggestion.frontend_id = autofill::POPUP_ITEM_ID_PASSWORD_ENTRY;
+    suggestion.match = prefix_matched_suggestion
+                           ? autofill::Suggestion::PREFIX_MATCH
+                           : autofill::Suggestion::SUBSTRING_MATCH;
+    suggestions->push_back(suggestion);
+  }
+}
+
 // This function attempts to fill |suggestions| and |realms| form |fill_data|
 // based on |current_username|. Unless |show_all| is true, it only picks
 // suggestions where the username has |current_username| as a prefix.
@@ -67,42 +94,28 @@ void GetSuggestions(const autofill::PasswordFormFillData& fill_data,
                     const base::string16& current_username,
                     std::vector<autofill::Suggestion>* suggestions,
                     bool show_all) {
-  base::string16 lower_username = base::i18n::ToLower(current_username);
-
-  if (show_all ||
-      base::StartsWith(base::i18n::ToLower(fill_data.username_field.value),
-                       lower_username, base::CompareCase::SENSITIVE)) {
-    autofill::Suggestion suggestion(
-        ReplaceEmptyUsername(fill_data.username_field.value));
-    suggestion.label = GetHumanReadableRealm(fill_data.preferred_realm);
-    suggestion.frontend_id = autofill::POPUP_ITEM_ID_PASSWORD_ENTRY;
-    suggestions->push_back(suggestion);
-  }
+  AppendSuggestionIfMatching(fill_data.username_field.value, current_username,
+                             fill_data.preferred_realm, show_all, suggestions);
 
   for (const auto& login : fill_data.additional_logins) {
-    if (show_all ||
-        base::StartsWith(base::i18n::ToLower(login.first), lower_username,
-                         base::CompareCase::SENSITIVE)) {
-      autofill::Suggestion suggestion(ReplaceEmptyUsername(login.first));
-      suggestion.label = GetHumanReadableRealm(login.second.realm);
-      suggestion.frontend_id = autofill::POPUP_ITEM_ID_PASSWORD_ENTRY;
-      suggestions->push_back(suggestion);
-    }
+    AppendSuggestionIfMatching(login.first, current_username,
+                               login.second.realm, show_all, suggestions);
   }
 
   for (const auto& usernames : fill_data.other_possible_usernames) {
     for (size_t i = 0; i < usernames.second.size(); ++i) {
-      if (show_all ||
-          base::StartsWith(base::i18n::ToLower(usernames.second[i]),
-                           lower_username, base::CompareCase::SENSITIVE)) {
-        autofill::Suggestion suggestion(
-            ReplaceEmptyUsername(usernames.second[i]));
-        suggestion.label = GetHumanReadableRealm(usernames.first.realm);
-        suggestion.frontend_id = autofill::POPUP_ITEM_ID_PASSWORD_ENTRY;
-        suggestions->push_back(suggestion);
-      }
+      AppendSuggestionIfMatching(usernames.second[i], current_username,
+                                 usernames.first.realm, show_all, suggestions);
     }
   }
+
+  // Prefix matches should precede other token matches.
+  if (autofill::IsFeatureSubstringMatchEnabled()) {
+    std::sort(suggestions->begin(), suggestions->end(),
+              [](const autofill::Suggestion& a, const autofill::Suggestion& b) {
+                return a.match < b.match;
+              });
+  }
 }
 
 }  // namespace
diff --git a/components/password_manager/core/browser/password_autofill_manager_unittest.cc b/components/password_manager/core/browser/password_autofill_manager_unittest.cc
index 7dd87dc..d214998 100644
--- a/components/password_manager/core/browser/password_autofill_manager_unittest.cc
+++ b/components/password_manager/core/browser/password_autofill_manager_unittest.cc
@@ -4,6 +4,7 @@
 
 #include "components/password_manager/core/browser/password_autofill_manager.h"
 
+#include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/message_loop/message_loop.h"
 #include "base/strings/utf_string_conversions.h"
@@ -12,6 +13,7 @@
 #include "components/autofill/core/browser/test_autofill_client.h"
 #include "components/autofill/core/browser/test_autofill_driver.h"
 #include "components/autofill/core/common/autofill_constants.h"
+#include "components/autofill/core/common/autofill_switches.h"
 #include "components/autofill/core/common/form_field_data.h"
 #include "components/autofill/core/common/password_form_fill_data.h"
 #include "components/password_manager/core/browser/stub_password_manager_client.h"
@@ -354,4 +356,180 @@ TEST_F(PasswordAutofillManagerTest, FillSuggestionPasswordField) {
       autofill::IS_PASSWORD_FIELD, element_bounds);
 }
 
+// Verify that typing "foo" into the username field will match usernames
+// "foo.bar@example.com", "bar.foo@example.com" and "example@foo.com".
+TEST_F(PasswordAutofillManagerTest, DisplaySuggestionsWithMatchingTokens) {
+  // Token matching is currently behind a flag.
+  base::CommandLine::ForCurrentProcess()->AppendSwitch(
+      autofill::switches::kEnableSuggestionsWithSubstringMatch);
+
+  scoped_ptr<TestPasswordManagerClient> client(new TestPasswordManagerClient);
+  scoped_ptr<MockAutofillClient> autofill_client(new MockAutofillClient);
+  InitializePasswordAutofillManager(client.get(), autofill_client.get());
+
+  gfx::RectF element_bounds;
+  autofill::PasswordFormFillData data;
+  base::string16 username = base::ASCIIToUTF16("foo.bar@example.com");
+  data.username_field.value = username;
+  data.password_field.value = base::ASCIIToUTF16("foobar");
+  data.preferred_realm = "http://foo.com/";
+
+  autofill::PasswordAndRealm additional;
+  additional.realm = "https://foobarrealm.org";
+  base::string16 additional_username(base::ASCIIToUTF16("bar.foo@example.com"));
+  data.additional_logins[additional_username] = additional;
+
+  autofill::UsernamesCollectionKey usernames_key;
+  usernames_key.realm = "http://yetanother.net";
+  std::vector<base::string16> other_names;
+  base::string16 other_username(base::ASCIIToUTF16("example@foo.com"));
+  other_names.push_back(other_username);
+  data.other_possible_usernames[usernames_key] = other_names;
+
+  int dummy_key = 0;
+  password_autofill_manager_->OnAddPasswordFormMapping(dummy_key, data);
+
+  EXPECT_CALL(
+      *autofill_client,
+      ShowAutofillPopup(element_bounds, _,
+                        SuggestionVectorValuesAre(testing::UnorderedElementsAre(
+                            username, additional_username, other_username)),
+                        _));
+  password_autofill_manager_->OnShowPasswordSuggestions(
+      dummy_key, base::i18n::RIGHT_TO_LEFT, base::ASCIIToUTF16("foo"), false,
+      element_bounds);
+}
+
+// Verify that typing "oo" into the username field will not match any usernames
+// "foo.bar@example.com", "bar.foo@example.com" or "example@foo.com".
+TEST_F(PasswordAutofillManagerTest, NoSuggestionForNonPrefixTokenMatch) {
+  // Token matching is currently behind a flag.
+  base::CommandLine::ForCurrentProcess()->AppendSwitch(
+      autofill::switches::kEnableSuggestionsWithSubstringMatch);
+
+  scoped_ptr<TestPasswordManagerClient> client(new TestPasswordManagerClient);
+  scoped_ptr<MockAutofillClient> autofill_client(new MockAutofillClient);
+  InitializePasswordAutofillManager(client.get(), autofill_client.get());
+
+  gfx::RectF element_bounds;
+  autofill::PasswordFormFillData data;
+  base::string16 username = base::ASCIIToUTF16("foo.bar@example.com");
+  data.username_field.value = username;
+  data.password_field.value = base::ASCIIToUTF16("foobar");
+  data.preferred_realm = "http://foo.com/";
+
+  autofill::PasswordAndRealm additional;
+  additional.realm = "https://foobarrealm.org";
+  base::string16 additional_username(base::ASCIIToUTF16("bar.foo@example.com"));
+  data.additional_logins[additional_username] = additional;
+
+  autofill::UsernamesCollectionKey usernames_key;
+  usernames_key.realm = "http://yetanother.net";
+  std::vector<base::string16> other_names;
+  base::string16 other_username(base::ASCIIToUTF16("example@foo.com"));
+  other_names.push_back(other_username);
+  data.other_possible_usernames[usernames_key] = other_names;
+
+  int dummy_key = 0;
+  password_autofill_manager_->OnAddPasswordFormMapping(dummy_key, data);
+
+  EXPECT_CALL(*autofill_client, ShowAutofillPopup(_, _, _, _)).Times(0);
+
+  password_autofill_manager_->OnShowPasswordSuggestions(
+      dummy_key, base::i18n::RIGHT_TO_LEFT, base::ASCIIToUTF16("oo"), false,
+      element_bounds);
+}
+
+// Verify that typing "foo@exam" into the username field will match username
+// "bar.foo@example.com" even if the field contents span accross multiple
+// tokens.
+TEST_F(PasswordAutofillManagerTest,
+       MatchingContentsWithSuggestionTokenSeparator) {
+  // Token matching is currently behind a flag.
+  base::CommandLine::ForCurrentProcess()->AppendSwitch(
+      autofill::switches::kEnableSuggestionsWithSubstringMatch);
+
+  scoped_ptr<TestPasswordManagerClient> client(new TestPasswordManagerClient);
+  scoped_ptr<MockAutofillClient> autofill_client(new MockAutofillClient);
+  InitializePasswordAutofillManager(client.get(), autofill_client.get());
+
+  gfx::RectF element_bounds;
+  autofill::PasswordFormFillData data;
+  base::string16 username = base::ASCIIToUTF16("foo.bar@example.com");
+  data.username_field.value = username;
+  data.password_field.value = base::ASCIIToUTF16("foobar");
+  data.preferred_realm = "http://foo.com/";
+
+  autofill::PasswordAndRealm additional;
+  additional.realm = "https://foobarrealm.org";
+  base::string16 additional_username(base::ASCIIToUTF16("bar.foo@example.com"));
+  data.additional_logins[additional_username] = additional;
+
+  autofill::UsernamesCollectionKey usernames_key;
+  usernames_key.realm = "http://yetanother.net";
+  std::vector<base::string16> other_names;
+  base::string16 other_username(base::ASCIIToUTF16("example@foo.com"));
+  other_names.push_back(other_username);
+  data.other_possible_usernames[usernames_key] = other_names;
+
+  int dummy_key = 0;
+  password_autofill_manager_->OnAddPasswordFormMapping(dummy_key, data);
+
+  EXPECT_CALL(
+      *autofill_client,
+      ShowAutofillPopup(element_bounds, _,
+                        SuggestionVectorValuesAre(
+                            testing::UnorderedElementsAre(additional_username)),
+                        _));
+  password_autofill_manager_->OnShowPasswordSuggestions(
+      dummy_key, base::i18n::RIGHT_TO_LEFT, base::ASCIIToUTF16("foo@exam"),
+      false, element_bounds);
+}
+
+// Verify that typing "example" into the username field will match and order
+// usernames "example@foo.com", "foo.bar@example.com" and "bar.foo@example.com"
+// i.e. prefix matched followed by substring matched.
+TEST_F(PasswordAutofillManagerTest,
+       DisplaySuggestionsWithPrefixesPrecedeSubstringMatched) {
+  // Token matching is currently behind a flag.
+  base::CommandLine::ForCurrentProcess()->AppendSwitch(
+      autofill::switches::kEnableSuggestionsWithSubstringMatch);
+
+  scoped_ptr<TestPasswordManagerClient> client(new TestPasswordManagerClient);
+  scoped_ptr<MockAutofillClient> autofill_client(new MockAutofillClient);
+  InitializePasswordAutofillManager(client.get(), autofill_client.get());
+
+  gfx::RectF element_bounds;
+  autofill::PasswordFormFillData data;
+  base::string16 username = base::ASCIIToUTF16("foo.bar@example.com");
+  data.username_field.value = username;
+  data.password_field.value = base::ASCIIToUTF16("foobar");
+  data.preferred_realm = "http://foo.com/";
+
+  autofill::PasswordAndRealm additional;
+  additional.realm = "https://foobarrealm.org";
+  base::string16 additional_username(base::ASCIIToUTF16("bar.foo@example.com"));
+  data.additional_logins[additional_username] = additional;
+
+  autofill::UsernamesCollectionKey usernames_key;
+  usernames_key.realm = "http://yetanother.net";
+  std::vector<base::string16> other_names;
+  base::string16 other_username(base::ASCIIToUTF16("example@foo.com"));
+  other_names.push_back(other_username);
+  data.other_possible_usernames[usernames_key] = other_names;
+
+  int dummy_key = 0;
+  password_autofill_manager_->OnAddPasswordFormMapping(dummy_key, data);
+
+  EXPECT_CALL(
+      *autofill_client,
+      ShowAutofillPopup(element_bounds, _,
+                        SuggestionVectorValuesAre(testing::UnorderedElementsAre(
+                            other_username, username, additional_username)),
+                        _));
+  password_autofill_manager_->OnShowPasswordSuggestions(
+      dummy_key, base::i18n::RIGHT_TO_LEFT, base::ASCIIToUTF16("foo"), false,
+      element_bounds);
+}
+
 }  // namespace password_manager
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 9daef96..7a95e99 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -60513,6 +60513,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="-964676765" label="enable-accelerated-mjpeg-decode"/>
   <int value="-951394314" label="top-chrome-md"/>
   <int value="-949178861" label="enable-new-avatar-menu"/>
+  <int value="-938178614" label="enable-suggestions-with-substring-match"/>
   <int value="-926422468" label="disable-embedded-shared-worker"/>
   <int value="-918618075" label="enable-service-worker"/>
   <int value="-914210146" label="enable-web-based-signin"/>