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

components/autofill/core/common/autofill_util.cc

Index: components/autofill/core/common/autofill_util.cc
diff --git a/components/autofill/core/common/autofill_util.cc b/components/autofill/core/common/autofill_util.cc
new file mode 100644
index 0000000000000000000000000000000000000000..8c0d7be01e525ce2b7fc60ecd681346a6d4b8105
--- /dev/null
+++ b/components/autofill/core/common/autofill_util.cc
@@ -0,0 +1,72 @@
+// 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 <vector>
+
+#include "base/command_line.h"
+#include "base/i18n/case_conversion.h"
+#include "base/strings/string_piece.h"
+#include "base/strings/string_util.h"
+#include "base/strings/utf_string_conversions.h"
+#include "components/autofill/core/common/autofill_switches.h"
+
+namespace autofill {
+
+bool IsFeatureSubstringMatchEnabled() {
+  return base::CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kEnableSuggestionsWithSubstringMatch);
+}
+
+bool IsContentsPrefixOfSuggestionToken(const base::string16& field_suggestion,
+                                       const base::string16& field_contents,
+                                       bool case_sensitive) {
+  if (!IsFeatureSubstringMatchEnabled()) {
+    return false;
+  }
+
+  bool result = false;
+  std::vector<base::string16> suggestion_tokens;
+  Tokenize(field_suggestion, base::ASCIIToUTF16(" .,-_@"), &suggestion_tokens);
+
+  // Check whether the |field_contents| prefixes any of the |field_suggestion|'s
+  // token.
+  for (auto token : suggestion_tokens) {
+    result = StartsWith(token, field_contents, case_sensitive);
+    if (result)
+      break;
+  }
+
+  return result;
+}
+
+base::string16::size_type ComputeRange(const base::string16& field_suggestion,
+                                       const base::string16& field_contents,
+                                       size_t* start,
+                                       size_t* end) {
+  base::string16::size_type offset = 0;
+  base::string16::size_type next_offset = 0;
+  do {
+    // Loop through until we find either the |field_contents| begins with the
+    // |suggestion| or character right before |offset| is one of the splitting
+    // characters.
+    base::string16 suggestion(field_suggestion.substr(next_offset));
+    offset = StartsAt(suggestion, field_contents, false);
+    if (base::string16::npos != offset) {
+      next_offset = offset + next_offset + 1;
+      if ((offset == 0) || ContainsOnlyChars(suggestion.substr(offset - 1, 1),
+                                             base::ASCIIToUTF16(" .,-_@"))) {
+        offset = next_offset - 1;
+        *start = offset + field_contents.size();
+        *end = field_suggestion.size();
+        break;
+      }
+    }
+  } while (base::string16::npos != offset);
+
+  return offset;
+}
+
+}  // namespace autofill