[BlobAsync] Adding better error reporting and some new tests.

storage/common/blob_storage/blob_storage_constants.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef STORAGE_COMMON_BLOB_STORAGE_BLOB_STORAGE_CONSTANTS_H_
 #define STORAGE_COMMON_BLOB_STORAGE_BLOB_STORAGE_CONSTANTS_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 16 matching lines @@
   FILE,
   LAST = FILE
 };
 
 // These items cannot be reordered or renumbered because they're recorded to
 // UMA. New items must be added immediately before LAST, and LAST must be set to
 // the the last item.
 enum class IPCBlobCreationCancelCode {
   UNKNOWN = 0,
   OUT_OF_MEMORY = 1,
+  // We couldn't create or write to a file. File system error, like a full hdd.

[jsbell, 2016/04/04 20:41:19]

nit: just say "disk"

[dmurph, 2016/04/04 22:17:42]

Done.

   FILE_WRITE_FAILED = 2,
   // The renderer was destroyed while data was in transit.
   SOURCE_DIED_IN_TRANSIT = 3,
   // The renderer destructed the blob before it was done transferring, and there
   // were no outstanding references (no one is waiting to read) to keep the
   // blob alive.
   BLOB_DEREFERENCED_WHILE_BUILDING = 4,
   // A blob that we referenced during construction is broken, or a browser-side
   // builder tries to build a blob with a blob reference that isn't finished
   // constructing.
   REFERENCED_BLOB_BROKEN = 5,
   LAST = REFERENCED_BLOB_BROKEN
 };
 
 }  // namespace storage
 
 #endif  // STORAGE_COMMON_BLOB_STORAGE_BLOB_STORAGE_CONSTANTS_H_