[Extensions Bindings] Add a bridge to use current custom bindings

extensions/renderer/string_source_map.cc

+// Copyright 2016 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 "extensions/renderer/string_source_map.h"
+
+#include "gin/converter.h"
+
+namespace extensions {
+
+StringSourceMap::StringSourceMap() {}
+StringSourceMap::~StringSourceMap() {}
+
+v8::Local<v8::String> StringSourceMap::GetSource(
+    v8::Isolate* isolate,
+    const std::string& name) const {
+  const auto& iter = sources_.find(name);
+  if (iter == sources_.end())
+    return v8::Local<v8::String>();
+  return gin::StringToV8(isolate, iter->second);
+}
+
+bool StringSourceMap::Contains(const std::string& name) const {
+  return sources_.find(name) != sources_.end();
+}
+
+void StringSourceMap::RegisterModule(const std::string& name,
+                                     const std::string& source) {
+  CHECK_EQ(0u, sources_.count(name)) << "Module " << name << " not found";

[jbroman, 2016/12/16 19:00:50]

Isn't the opposite the problem, that the module _was_ already found in
|sources_|?

[Devlin, 2016/12/16 20:31:17]

Copy-paste code strikes again!  It was this way in module_system_test.cc, too. 
Fixed.

+  sources_[name] = source;
+}
+
+}  // namespace extensions