Remove CaseInsensitiveCompare from string_util.h

There were a number of callers in net using this for HTTP headers. I think
these callers actually just need ASCII case-insensitive comparisons so these
were changed.

The omnibox code used this functor. I added a new omnibox-specific one which
does not have the locale issues of the old string_util one, but which still
has the UTF-16 and combining accent issues (described in great detail in
the comment for this).

The Windows installer code can't depend on ICU so it calls the Win32 function
to do case-insensitive comparisons. This should match the system comparison
for registry keys better anyway.

I also changed a caller of StartsWith to use this version. I wrote this
StartsWith call using ToLower in a previous patch, but it turns out that the
lengths of case-mapped strings do change in practice, making the offset
computations of the suyrrounding code incorrect. This new version will be
like the old version (will miss some cases of case-insensitive equality) but
will handle 0x80-0xFF properly.

BUG=24917

Review URL: https://codereview.chromium.org/1230583014

Cr-Commit-Position: refs/heads/master@{#338624}

3 files changed, 49 insertions, 4 deletions

diff --git a/components/omnibox/browser/autocomplete_i18n.h b/components/omnibox/browser/autocomplete_i18n.h
new file mode 100644
index 0000000..9733e17
--- /dev/null
+++ b/components/omnibox/browser/autocomplete_i18n.h
@@ -0,0 +1,41 @@
+// 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_OMNIBOX_BROWSER_AUTOCOMPLETE_I18N_H_
+#define COMPONENTS_OMNIBOX_BROWSER_AUTOCOMPLETE_I18N_H_
+
+#include "base/strings/string16.h"
+#include "third_party/icu/source/common/unicode/uchar.h"
+
+// Functor for a simple 16-bit Unicode case-insensitive comparison. This is
+// designed for the autocomplete system where we would rather get prefix lenths
+// correct than handle all possible case sensitivity issues.
+//
+// Any time this is used the result will be incorrect in some cases that
+// certain users will be able to discern. Ideally, this class would be deleted
+// and we would do full Unicode case-sensitivity mappings using
+// base::i18n::ToLower. However, ToLower can change the lenghts of strings,
+// making computations of offsets or prefix lengths difficult. Getting all
+// edge cases correct will require careful implementation and testing. In the
+// mean time, we use this simpler approach.
+//
+// This comparator will not handle combining accents properly since it compares
+// 16-bit values in isolation. If the two strings use the same sequence of
+// combining accents (this is the normal case) in both strings, it will work.
+//
+// Additionally, this comparator does not decode UTF sequences which is why it
+// is called "UCS2". UTF-16 surrogates will be compared literally (i.e. "case-
+// sensitively").
+//
+// There are also a few cases where the lower-case version of a character
+// expands to more than one code point that will not be handled properly. Such
+// characters will be compared case-sensitively.
+struct SimpleCaseInsensitiveCompareUCS2 {
+ public:
+  bool operator()(base::char16 x, base::char16 y) const {
+    return u_tolower(x) == u_tolower(y);
+  }
+};
+
+#endif  // COMPONENTS_OMNIBOX_BROWSER_AUTOCOMPLETE_I18N_H_
diff --git a/components/omnibox/browser/search_suggestion_parser.cc b/components/omnibox/browser/search_suggestion_parser.cc
index 9c411fc..11fbdbb 100644
--- a/components/omnibox/browser/search_suggestion_parser.cc
+++ b/components/omnibox/browser/search_suggestion_parser.cc
@@ -15,6 +15,7 @@
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/values.h"
+#include "components/omnibox/browser/autocomplete_i18n.h"
 #include "components/omnibox/browser/autocomplete_input.h"
 #include "components/omnibox/browser/url_prefix.h"
 #include "components/url_fixer/url_fixer.h"
@@ -158,7 +159,7 @@ void SearchSuggestionParser::SuggestResult::ClassifyMatchContents(
   // Do a case-insensitive search for |lookup_text|.
   base::string16::const_iterator lookup_position = std::search(
       match_contents_.begin(), match_contents_.end(), lookup_text.begin(),
-      lookup_text.end(), base::CaseInsensitiveCompare<base::char16>());
+      lookup_text.end(), SimpleCaseInsensitiveCompareUCS2());
   if (!allow_bolding_all && (lookup_position == match_contents_.end())) {
     // Bail if the code below to update the bolding would bold the whole
     // string.  Note that the string may already be entirely bolded; if
diff --git a/components/omnibox/browser/shortcuts_provider.cc b/components/omnibox/browser/shortcuts_provider.cc
index 962cc13..8d43be6 100644
--- a/components/omnibox/browser/shortcuts_provider.cc
+++ b/components/omnibox/browser/shortcuts_provider.cc
@@ -20,6 +20,7 @@
 #include "base/time/time.h"
 #include "components/history/core/browser/history_service.h"
 #include "components/metrics/proto/omnibox_input_type.pb.h"
+#include "components/omnibox/browser/autocomplete_i18n.h"
 #include "components/omnibox/browser/autocomplete_input.h"
 #include "components/omnibox/browser/autocomplete_match.h"
 #include "components/omnibox/browser/autocomplete_provider_client.h"
@@ -218,9 +219,11 @@ AutocompleteMatch ShortcutsProvider::ShortcutToACMatch(
   // input of "foo.c" to autocomplete to "foo.com" for a fill_into_edit of
   // "http://foo.com".
   if (AutocompleteMatch::IsSearchType(match.type)) {
-    if (base::StartsWith(base::i18n::ToLower(match.fill_into_edit),
-                         base::i18n::ToLower(input.text()),
-                         base::CompareCase::SENSITIVE)) {
+    if (match.fill_into_edit.size() >= input.text().size() &&
+        std::equal(match.fill_into_edit.begin(),
+                   match.fill_into_edit.begin() + input.text().size(),
+                   input.text().begin(),
+                   SimpleCaseInsensitiveCompareUCS2())) {
       match.inline_autocompletion =
           match.fill_into_edit.substr(input.text().length());
       match.allowed_to_be_default_match =