Code:  void FileBrowserHandlerCustomBindings::GetExternalFileEntry(
    const v8::FunctionCallbackInfo<v8::Value>& args) {
//// TODO(zelidrag): Make this magic work on other platforms when file browser
//// matures enough on ChromeOS.
 #if defined(OS_CHROMEOS)
     CHECK(args.Length() == 1);
     CHECK(args[0]->IsObject());
    v8::Local<v8::Object> file_def = args[0]->ToObject();
    std::string file_system_name(
        *v8::String::Utf8Value(file_def->Get(
            v8::String::NewFromUtf8(args.GetIsolate(), "fileSystemName"))));
    GURL file_system_root(
        *v8::String::Utf8Value(file_def->Get(
            v8::String::NewFromUtf8(args.GetIsolate(), "fileSystemRoot"))));
    std::string file_full_path(
        *v8::String::Utf8Value(file_def->Get(
            v8::String::NewFromUtf8(args.GetIsolate(), "fileFullPath"))));
    bool is_directory = file_def->Get(v8::String::NewFromUtf8(
        args.GetIsolate(), "fileIsDirectory"))->ToBoolean()->Value();
    blink::WebDOMFileSystem::EntryType entry_type =
         is_directory ? blink::WebDOMFileSystem::EntryTypeDirectory
                      : blink::WebDOMFileSystem::EntryTypeFile;
     blink::WebLocalFrame* webframe =
        blink::WebLocalFrame::frameForContext(context()->v8_context());
     args.GetReturnValue().Set(
         blink::WebDOMFileSystem::create(
             webframe,
            blink::WebFileSystemTypeExternal,
            blink::WebString::fromUTF8(file_system_name),
            file_system_root)
            .createV8Entry(blink::WebString::fromUTF8(file_full_path),
                           entry_type,
                           args.Holder(),
                           args.GetIsolate()));
 #endif
 }

Vulnerability Type: Bypass 
CWE ID: 
Summary: The extensions subsystem in Google Chrome before 51.0.2704.63 allows remote attackers to bypass the Same Origin Policy via unspecified vectors.
Commit Message: [Extensions] Add more bindings access checks

BUG=598165

Review URL: https://codereview.chromium.org/1854983002

Cr-Commit-Position: refs/heads/master@{#385282}