[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 == '$' && i + 1 < format_string.end() && i[1] == '{') {
+      size_t key_start = i + strlen("${") - format_string.begin();
+      size_t key_length = format_string.find('}', key_start);
+      if (key_length == base::StringPiece::npos)
+        NOTREACHED() << "TemplateExpression missing ending brace '}'";
+      key_length -= key_start;
+      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 += strlen("${") + key_length + strlen("}");
+        continue;
+      } else {
+        NOTREACHED() << "TemplateExpression key not found: " << key;
+      }
+    }
+    formatted.push_back(*i);
+    ++i;
+  }
+  return formatted;
+}
+
+}  // namespace ui