Add isWritableFileEntry to the fileSystem API

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

Index: chrome/browser/extensions/api/file_system/file_system_api.cc
diff --git a/chrome/browser/extensions/api/file_system/file_system_api.cc b/chrome/browser/extensions/api/file_system/file_system_api.cc
index 3288e8a9dbfccb1b06af938be06a5452b382ff32..c3c71250251315d4ac4dcef171458bd5ac568ac0 100644
--- a/chrome/browser/extensions/api/file_system/file_system_api.cc
+++ b/chrome/browser/extensions/api/file_system/file_system_api.cc
@@ -7,6 +7,7 @@
 #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"
@@ -236,6 +237,28 @@ bool FileSystemGetWritableFileEntryFunction::RunImpl() {
   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