Fix filesystem API file_handlers to work for drive on ChromeOS.

chrome/browser/chromeos/drive/drive_file_system_proxy.cc

Index: chrome/browser/chromeos/drive/drive_file_system_proxy.cc
diff --git a/chrome/browser/chromeos/drive/drive_file_system_proxy.cc b/chrome/browser/chromeos/drive/drive_file_system_proxy.cc
index 6a616508d9bc2d70940b190af5ccd2646b05cbe9..567cfa74eb16c6ead1cddcf9f606a9ac0971a6ea 100644
--- a/chrome/browser/chromeos/drive/drive_file_system_proxy.cc
+++ b/chrome/browser/chromeos/drive/drive_file_system_proxy.cc
@@ -179,6 +179,7 @@ void DriveFileSystemProxy::DetachFromFileSystem() {
 void DriveFileSystemProxy::GetFileInfo(const FileSystemURL& file_url,
     const FileSystemOperation::GetMetadataCallback& callback) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+
   base::FilePath file_path;
   if (!ValidateUrl(file_url, &file_path)) {
     MessageLoopProxy::current()->PostTask(FROM_HERE,
@@ -697,8 +698,13 @@ bool DriveFileSystemProxy::ValidateUrl(
   if (!url.is_valid() || url.type() != fileapi::kFileSystemTypeDrive) {
     return false;
   }
-  *file_path = url.virtual_path();
-  return true;
+
+  // |url.virtual_path()| cannot be used directly because in the case the url is
+  // isolated file system url, the virtual path will be formatted as
+  // <isolated_file_system_id>/<file_name> and thus unusable by drive file
+  // system.
+  *file_path = util::ExtractDrivePath(url.path());
+  return !file_path->empty();
 }
 
 void DriveFileSystemProxy::CallDriveFileSystemMethodOnUIThread(