[ui/base;css] adding string template expression replacement

ui/base/template_expressions.cc

+// 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 "ui/base/template_expressions.h"
+
+#include "base/logging.h"
+
+namespace ui {
+
+std::string ReplaceTemplateExpressions(
+    base::StringPiece format_string,
+    const std::map<base::StringPiece, std::string>& substitutions) {
+  std::string formatted;
+  const size_t kValueLengthGuess = 16;
+  formatted.reserve(format_string.length() +
+                    substitutions.size() * kValueLengthGuess);
+  base::StringPiece::const_iterator i = format_string.begin();
+  while (i < format_string.end()) {
+    if (*i == '$' && i < format_string.end() && i[1] == '{') {

[Nico, 2015/07/16 20:34:00]

you want `i + 1 < format_string.end()` here I think (if so, add test coverage
for this case)

[dschuyler, 2015/07/16 20:57:14]

There already is a test case that would go past the end, but it does not cause
issue because it's still valid memory to read from.  This would be an issue if
the last character before an inaccessible page of memory was a '$'.

Done.

+      size_t key_start = i + 2 - format_string.begin();

[Nico, 2015/07/16 20:34:00]

s/2/strlen("${")

[dschuyler, 2015/07/16 20:57:14]

Done.

+      size_t key_length = format_string.find('}', key_start) - key_start;

[Nico, 2015/07/16 20:34:00]

find() returns npos on not found, which becomes a very large size_t. Check that
'}' was actually found (and add test coverage for this)

[dschuyler, 2015/07/16 20:57:14]

Done.

+      base::StringPiece key(format_string.begin() + key_start, key_length);
+      const auto& replacement = substitutions.find(key);
+      if (replacement != substitutions.end()) {
+        formatted.append(replacement->second);
+        i += key_length + 3;

[Nico, 2015/07/16 20:34:00]

s/3/strlen("${}")

[dschuyler, 2015/07/16 20:57:14]

Done.

+        continue;
+      } else {
+        NOTREACHED() << "TemplateExpression key not found: " << key;
+      }
+    }
+    formatted.push_back(*i);
+    ++i;
+  }
+  return formatted;
+}
+
+}  // namespace ui