Fixed the bug that Drive doesn't appear on Files App on epehmeral mode.

components/drive/chromeos/file_cache.cc

Index: components/drive/chromeos/file_cache.cc
diff --git a/components/drive/chromeos/file_cache.cc b/components/drive/chromeos/file_cache.cc
index 1e6c145d8124d6ff25c04a5f50d414ace9e35c8b..b5a2f1f2b8870790d7f9472716c6ade89100f49f 100644
--- a/components/drive/chromeos/file_cache.cc
+++ b/components/drive/chromeos/file_cache.cc
@@ -52,6 +52,16 @@ base::FilePath GetPathForId(const base::FilePath& cache_directory,
       base::FilePath::FromUTF8Unsafe(util::EscapeCacheFileName(id)));
 }
 
+// Returns if the filesystem backing |path| supports file attributes.
+// This will return false if the filesystem is for example tmpfs, which is used
+// for ephemeral mode.
+bool IsFileAttributesSupported(const base::FilePath& path) {
+  if (getxattr(path.value().c_str(), "user.foo", nullptr, 0) >= 0) {
+    return true;
+  }
+  return errno != ENOTSUP;
+}
+
 // Sets extended file attribute as |name| |value| pair.
 bool SetExtendedFileAttributes(const base::FilePath& path,
     const std::string& name, const std::string& value) {
@@ -92,8 +102,14 @@ FileAttributes GetFileAttributes(const base::FilePath& path) {
   return flags;
 }
 
-// Marks the cache file to be removable by cryptohome.
+// Marks the cache file to be removable by cryptohome, or do nothing if
+// underlying filesystem doesn't support file attributes, as tmpfs for ephemeral
+// mode.
 bool SetRemovable(const base::FilePath& path) {
+  // For ephemeral mode.
+  if (!IsFileAttributesSupported(path)) {
+    return true;
+  }
   FileAttributes flags = GetFileAttributes(path);
   if (flags < 0) return false;
   if ((flags & FS_NODUMP_FL) == FS_NODUMP_FL) return true;
@@ -101,8 +117,14 @@ bool SetRemovable(const base::FilePath& path) {
   return SetFileAttributes(path, flags | FS_NODUMP_FL);
 }
 
-// Marks the cache file to be unremovable by cryptohome.
+// Marks the cache file to be unremovable by cryptohome, or do nothing if
+// underlying filesystem doesn't support file attributes, as tmpfs for ephemeral
+// mode.
 bool UnsetRemovable(const base::FilePath& path) {
+  // For ephemeral mode.
+  if (!IsFileAttributesSupported(path)) {
+    return true;
+  }
   FileAttributes flags = GetFileAttributes(path);
   if (flags < 0) return false;
   if ((flags & FS_NODUMP_FL) == 0) return true;
@@ -110,9 +132,14 @@ bool UnsetRemovable(const base::FilePath& path) {
   return SetFileAttributes(path, flags & ~FS_NODUMP_FL);
 }
 
-// Marks |path| as drive cache dir.
-// Returns if the operation succeeded.
+// Marks |path| as drive cache dir, or do nothing if underlying filesystem
+// doesn't support file attributes, as tmpfs for ephemeral mode. Returns if the
+// operation succeeded.
 bool MarkAsDriveCacheDir(const base::FilePath& path) {
+  // For ephemeral mode.
+  if (!IsFileAttributesSupported(path)) {
+    return true;
+  }
   return SetRemovable(path)
       && SetExtendedFileAttributes(path, FileCache::kGCacheFilesAttribute, "");
 }