Updated error translation logic.

base/ios/ns_error_util.mm

Index: base/ios/ns_error_util.mm
diff --git a/base/ios/ns_error_util.mm b/base/ios/ns_error_util.mm
new file mode 100644
index 0000000000000000000000000000000000000000..c44d9ee4135c469fa241907d7ed8704bbfcb611b
--- /dev/null
+++ b/base/ios/ns_error_util.mm
@@ -0,0 +1,53 @@
+// 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.
+
+#import "base/ios/ns_error_util.h"
+
+#import <Foundation/Foundation.h>
+
+#include "base/logging.h"
+#include "base/mac/scoped_nsobject.h"
+
+namespace base {
+namespace ios {
+
+namespace {
+// Iterates through |error|'s underlying errors and returns them in an array.
+NSArray* GetFullErrorChainForError(NSError* error) {
+  NSMutableArray* error_chain = [NSMutableArray array];
+  NSError* current_error = error;
+  while (current_error) {
+    DCHECK([current_error isKindOfClass:[NSError class]]);
+    [error_chain addObject:current_error];
+    current_error = current_error.userInfo[NSUnderlyingErrorKey];
+  }
+  return error_chain;
+}
+}  // namespace
+
+NSError* GetFinalUnderlyingErrorFromError(NSError* error) {
+  DCHECK(error);
+  return [GetFullErrorChainForError(error) lastObject];
+}
+
+NSError* ErrorWithAppendedUnderlyingError(NSError* original_error,
+                                          NSError* underlying_error) {
+  DCHECK(original_error);
+  DCHECK(underlying_error);
+  NSArray* error_chain = GetFullErrorChainForError(original_error);
+  NSError* current_error = underlying_error;
+  for (NSInteger idx = error_chain.count - 1; idx >= 0; --idx) {
+    NSError* error = error_chain[idx];
+    scoped_nsobject<NSMutableDictionary> user_info(
+        [error.userInfo mutableCopy]);
+    [user_info setObject:current_error forKey:NSUnderlyingErrorKey];
+    current_error = [NSError errorWithDomain:error.domain
+                                        code:error.code
+                                    userInfo:user_info];
+  }
+  return current_error;
+}
+
+}  // namespace ios
+}  // namespace base