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..bb6865f73e6de15b9eb084eea9e56ce93ed1cd78 100644
--- a/components/drive/chromeos/file_cache.cc
+++ b/components/drive/chromeos/file_cache.cc
@@ -52,9 +52,20 @@ 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) {
+  getxattr(path.value().c_str(), "user.foo", nullptr, 0);

[hashimoto, 2016/10/14 04:16:49]

Please check that getxattr actually fails.

[oka, 2016/10/14 04:36:06]

Done.

+  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) {
+  if (!IsFileAttributesSupported(path)) {

[hashimoto, 2016/10/14 04:16:49]

Isn't it better to check this at the beginning of MarkAsDriveCacheDir instead?

[oka, 2016/10/14 04:36:05]

Done.

+    return true;
+  }
   return setxattr(path.value().c_str(), name.c_str(), value.c_str(),
       value.size() + 1, 0) == 0;
 }
@@ -94,6 +105,9 @@ FileAttributes GetFileAttributes(const base::FilePath& path) {
 
 // Marks the cache file to be removable by cryptohome.
 bool SetRemovable(const base::FilePath& path) {
+  if (!IsFileAttributesSupported(path)) {

[hashimoto, 2016/10/14 04:16:48]

It'd be nice to have a brief comment to justify this early-return.

[oka, 2016/10/14 04:36:05]

Done.

+    return true;
+  }
   FileAttributes flags = GetFileAttributes(path);
   if (flags < 0) return false;
   if ((flags & FS_NODUMP_FL) == FS_NODUMP_FL) return true;
@@ -103,6 +117,9 @@ bool SetRemovable(const base::FilePath& path) {
 
 // Marks the cache file to be unremovable by cryptohome.
 bool UnsetRemovable(const base::FilePath& path) {
+  if (!IsFileAttributesSupported(path)) {

[hashimoto, 2016/10/14 04:16:48]

ditto.

[oka, 2016/10/14 04:36:06]

Done.

+    return true;
+  }
   FileAttributes flags = GetFileAttributes(path);
   if (flags < 0) return false;
   if ((flags & FS_NODUMP_FL) == 0) return true;