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..bd0b17f2e4bc7a75b2739ae7db42bba3be8a05f1 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 +956,37 @@ void FileManagerPrivateInternalSetEntryTagFunction::OnSetEntryPropertyCompleted(
                                          : Error("Failed to set a tag."));
 }
 
+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");

[mtomasz, 2016/09/01 07:49:49]

nit: period missing.

[harukam, 2016/09/02 01:33:32]

You can also find line 804 missing period.
Should I correct it as well as this?

[mtomasz, 2016/09/02 01:36:37]

Up to you. It's a minor thing, but if possible we should try to be consistent.

[harukam, 2016/09/02 03:45:38]

Thanks, I've added a period 804 line.

+    return false;
+  }
+
+  const base::FilePath root_path = file_manager::util::GetLocalPathFromURL(
+      render_frame_host(), GetProfile(), GURL(params->url));
+
+  if (root_path.empty())

[mtomasz, 2016/09/01 07:49:48]

nit: Maybe we should set an error message?

[harukam, 2016/09/02 01:33:32]

Acknowledged.

+    return false;
+
+  base::PostTaskAndReplyWithResult(
+      BrowserThread::GetBlockingPool(), FROM_HERE,
+      base::Bind(&base::ComputeDirectorySize, root_path),

[mtomasz, 2016/09/01 07:49:49]

Does it work on non native mount points, eg. on Drive or on Dropbox (via FSP
API)? If it's not intended to work, then can we add a comment?

[harukam, 2016/09/02 01:33:32]

It works only on local directories, not on Drive.
We will get Drive directories' size in another way.
To check whether the url is local, I added several lines above.

+      base::Bind(&FileManagerPrivateInternalGetDirectorySizeFunction::
+                     OnDirectorySizeRetrieved,
+                 this));
+  return true;
+}
+
+void FileManagerPrivateInternalGetDirectorySizeFunction::
+    OnDirectorySizeRetrieved(int64_t size) {
+  SetResult(
+      base::MakeUnique<base::FundamentalValue>(static_cast<double>(size)));
+  SendResponse(true);
+}
+
 }  // namespace extensions