Add isWritableFileEntry to the fileSystem API

chrome/browser/extensions/api/file_system/file_system_api.cc

 // Copyright (c) 2012 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 "chrome/browser/extensions/api/file_system/file_system_api.h"
 
 #include "base/bind.h"
 #include "base/file_path.h"
 #include "base/file_util.h"
+#include "base/logging.h"
 #include "base/path_service.h"
 #include "base/utf_string_conversions.h"
 #include "chrome/browser/extensions/shell_window_registry.h"
 #include "chrome/browser/platform_util.h"
 #include "chrome/browser/ui/chrome_select_file_policy.h"
 #include "chrome/browser/ui/extensions/shell_window.h"
 #include "chrome/common/extensions/api/file_system.h"
 #include "chrome/common/extensions/permissions/api_permission.h"
 #include "content/public/browser/child_process_security_policy.h"
 #include "content/public/browser/render_view_host.h"
@@ skipping 209 matching lines @@
   if (!GetFilePathOfFileEntry(filesystem_name, filesystem_path,
                               render_view_host_, &path, &error_))
     return false;
 
   content::BrowserThread::PostTask(content::BrowserThread::FILE, FROM_HERE,
       base::Bind(&FileSystemGetWritableFileEntryFunction::CheckWritableFile,
           this, path));
   return true;
 }
 
+bool FileSystemIsWritableFileEntryFunction::RunImpl() {
+  std::string filesystem_name;
+  std::string filesystem_path;
+  EXTENSION_FUNCTION_VALIDATE(args_->GetString(0, &filesystem_name));
+  EXTENSION_FUNCTION_VALIDATE(args_->GetString(1, &filesystem_path));
+
+  std::string filesystem_id;
+  if (!fileapi::CrackIsolatedFileSystemName(filesystem_name, &filesystem_id)) {
+    error_ = kInvalidParameters;
+    return false;
+  }
+
+  content::ChildProcessSecurityPolicy* policy =
+      content::ChildProcessSecurityPolicy::GetInstance();
+  int renderer_id = render_view_host_->GetProcess()->GetID();
+  bool is_writable = policy->CanReadWriteFileSystem(renderer_id,
+                                                    filesystem_id);
+
+  SetResult(base::Value::CreateBooleanValue(is_writable));
+  return true;
+}
+
 // Handles showing a dialog to the user to ask for the filename for a file to
 // save or open.
 class FileSystemChooseFileFunction::FilePicker
     : public SelectFileDialog::Listener {
  public:
   FilePicker(FileSystemChooseFileFunction* function,
              content::WebContents* web_contents,
              const FilePath& suggested_name,
              SelectFileDialog::Type picker_type,
              EntryType entry_type)
@@ skipping 159 matching lines @@
 
   if (entry_type == WRITABLE && !HasFileSystemWritePermission()) {
     error_ = kRequiresFileSystemWriteError;
     return false;
   }
 
   return ShowPicker(suggested_name, picker_type, entry_type);
 }
 
 }  // namespace extensions