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

ui/base/template_expressions.cc

Index: ui/base/template_expressions.cc
diff --git a/ui/base/template_expressions.cc b/ui/base/template_expressions.cc
new file mode 100644
index 0000000000000000000000000000000000000000..ae0ce2856a1c643dab7adc16a4e96b6d93c62c1a
--- /dev/null
+++ b/ui/base/template_expressions.cc
@@ -0,0 +1,56 @@
+// 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"
+#include "base/strings/utf_string_conversions.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 == '$') {
+      ++i;
+      if (i < format_string.end()) {
+        if (*i == '{') {
+          ++i;
+          std::string index;
+          while (i < format_string.end()) {
+            if (*i == '}') {
+              ++i;
+              break;
+            }
+            index.push_back(*i);
+            ++i;
+          }
+          const auto& replacement = substitutions.find(index);
+          if (replacement != substitutions.end()) {
+            formatted.append(replacement->second);
+          } else {
+            // NOTREACHED() << "Missing template expression " << index;
+          }
+        } else if (*i == '$') {
+          while (i < format_string.end() && *i == '$') {
+            formatted.push_back('$');
+            ++i;
+          }
+        }
+      }
+    } else {
+      formatted.push_back(*i);
+      ++i;
+    }
+  }
+  return formatted;
+}
+
+}  // namespace ui