arc: Use the MIME type returned by the container to handle content URLs

chrome/browser/chromeos/arc/fileapi/arc_file_system_operation_runner.cc

Index: chrome/browser/chromeos/arc/fileapi/arc_file_system_operation_runner.cc
diff --git a/chrome/browser/chromeos/arc/fileapi/arc_file_system_operation_runner.cc b/chrome/browser/chromeos/arc/fileapi/arc_file_system_operation_runner.cc
index 77bcfeb059b48412225f16d1ec23118b0943a431..4e8c0d0bf9c2eb2c7e1fad2fd8388a6b547d9f50 100644
--- a/chrome/browser/chromeos/arc/fileapi/arc_file_system_operation_runner.cc
+++ b/chrome/browser/chromeos/arc/fileapi/arc_file_system_operation_runner.cc
@@ -104,6 +104,26 @@ void ArcFileSystemOperationRunner::GetFileSize(
   file_system_instance->GetFileSize(url.spec(), callback);
 }
 
+void ArcFileSystemOperationRunner::GetMimeType(
+    const GURL& url,
+    const GetMimeTypeCallback& callback) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  if (should_defer_) {
+    deferred_operations_.emplace_back(
+        base::Bind(&ArcFileSystemOperationRunner::GetMimeType,
+                   weak_ptr_factory_.GetWeakPtr(), url, callback));
+    return;
+  }
+  auto* file_system_instance = ARC_GET_INSTANCE_FOR_METHOD(
+      arc_bridge_service()->file_system(), GetMimeType);
+  if (!file_system_instance) {
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE, base::Bind(callback, base::Optional<std::string>()));

[dcheng, 2017/06/01 11:06:44]

Let's use base::nullopt instead of base::Optional<T>()

[hashimoto, 2017/06/01 11:30:16]

Sounds good.
Done.

+    return;
+  }
+  file_system_instance->GetMimeType(url.spec(), callback);
+}
+
 void ArcFileSystemOperationRunner::OpenFileToRead(
     const GURL& url,
     const OpenFileToReadCallback& callback) {