Add API to get a folder's size.

chrome/browser/chromeos/extensions/file_manager/private_api_file_system.cc

Index: chrome/browser/chromeos/extensions/file_manager/private_api_file_system.cc
diff --git a/chrome/browser/chromeos/extensions/file_manager/private_api_file_system.cc b/chrome/browser/chromeos/extensions/file_manager/private_api_file_system.cc
index 0cdc8c6702629349dec42dbf0bf85b62bb1a366d..188748c2b72285c443b87e9d2bd3846f32889f56 100644
--- a/chrome/browser/chromeos/extensions/file_manager/private_api_file_system.cc
+++ b/chrome/browser/chromeos/extensions/file_manager/private_api_file_system.cc
@@ -11,6 +11,7 @@
 #include <utility>
 #include <vector>
 
+#include "base/files/file_util.h"
 #include "base/memory/ptr_util.h"
 #include "base/memory/weak_ptr.h"
 #include "base/posix/eintr_wrapper.h"
@@ -955,4 +956,29 @@ void FileManagerPrivateInternalSetEntryTagFunction::OnSetEntryPropertyCompleted(
                                          : Error("Failed to set a tag."));
 }
 
+FileManagerPrivateInternalGetDirectorySizeFunction::
+    FileManagerPrivateInternalGetDirectorySizeFunction()
+    : chrome_details_(this) {}
+
+bool FileManagerPrivateInternalGetDirectorySizeFunction::RunAsync() {
+  using extensions::api::file_manager_private_internal::GetDirectorySize::
+      Params;
+  const std::unique_ptr<Params> params(Params::Create(*args_));
+  EXTENSION_FUNCTION_VALIDATE(params);
+
+  if (params->url.empty()) {
+    SetError("File URL must be provided");
+    return false;
+  }
+
+  const base::FilePath root_path = file_manager::util::GetLocalPathFromURL(

[fukino, 2016/08/30 05:17:06]

Please check if the root_path is empty or not.

[harukam, 2016/08/30 06:33:41]

Done.

+      render_frame_host(), chrome_details_.GetProfile(), GURL(params->url));

[fukino, 2016/08/30 05:17:06]

chrome_details_ looks unnecessary. Simply GetProfile() should work.

[harukam, 2016/08/30 06:33:41]

Acknowledged.

+  int64_t size = base::ComputeDirectorySize(root_path);

[fukino, 2016/08/30 05:17:06]

You should not access file system on this thread not to block the UI.
BlockingPool is the preferred thread for such purpose.

You can refer to
FileManagerPrivateInternalValidatePathNameLengthFunction::RunAsync() to touch
file system on blocking pool.

[harukam, 2016/08/30 06:33:42]

Acknowledged.

+
+  SetResult(
+      base::MakeUnique<base::FundamentalValue>(static_cast<double>(size)));
+  SendResponse(true);
+  return true;
+}
+
 }  // namespace extensions