Fix crash in DirectoryImpl::Flush()

BUG=None

Review-Url: https://codereview.chromium.org/2604843002
Cr-Commit-Position: refs/heads/master@{#440858}

components/filesystem/directory_impl.cc

@@ -224,7 +224,8 @@ void DirectoryImpl::IsWritable(const std::string& raw_path,
 }
 
 void DirectoryImpl::Flush(const FlushCallback& callback) {
-  base::File file(directory_path_, base::File::FLAG_READ);
+  base::File file(directory_path_,
+                  base::File::FLAG_OPEN | base::File::FLAG_READ);
   if (!file.IsValid()) {
     callback.Run(GetError(file));
     return;

components/filesystem/directory_impl_unittest.cc

@@ -276,6 +276,18 @@ TEST_F(DirectoryImplTest, CantWriteFileOnADirectory) {
   }
 }
 
+TEST_F(DirectoryImplTest, Flush) {
+  mojom::DirectoryPtr directory;
+  GetTemporaryRoot(&directory);
+  mojom::FileError error;
+
+  {
+    bool handled = directory->Flush(&error);
+    ASSERT_TRUE(handled);
+    EXPECT_EQ(mojom::FileError::OK, error);
+  }
+}
+
 // TODO(vtl): Test delete flags.
 
 }  // namespace