Eliminate silently letting errors pass on pak loading.

ui/base/resource/resource_bundle_mac.mm

 // Copyright (c) 2012 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.
 
 #include "ui/base/resource/resource_bundle.h"
 
 #import <AppKit/AppKit.h>
 
 #include "base/basictypes.h"
 #include "base/files/file_path.h"
@@ skipping 21 matching lines @@
     resource_path = [base::mac::FrameworkBundle() pathForResource:name
                                                            ofType:@"pak"
                                                       inDirectory:@""
                                                   forLocalization:mac_locale];
   } else {
     resource_path = [base::mac::FrameworkBundle() pathForResource:name
                                                            ofType:@"pak"];
   }
 
   if (!resource_path) {
-    // Return just the name of the pack file.
-    return base::FilePath(base::SysNSStringToUTF8(name) + ".pak");
+    // Trying to load a resources file that doesn't exist is an error. Return
+    // just the name of the pack file so that further down the line it is easier
+    // to track down what happened.
+    std::string name_string = base::SysNSStringToUTF8(name);
+    std::string locale_string = base::SysNSStringToUTF8(mac_locale);
+    LOG(ERROR) << "Tried to get the file path of a non-existent pak file '"
+               << name_string << "' for locale '" << locale_string << "'";
+    return base::FilePath(name_string + ".pak");
   }
 
   return base::FilePath([resource_path fileSystemRepresentation]);
 }
 
 }  // namespace
 
 void ResourceBundle::LoadCommonResources() {
   AddDataPackFromPath(GetResourcesPakFilePath(@"chrome_100_percent",
                         nil), SCALE_FACTOR_100P);
@@ skipping 90 matching lines @@
 
   // Another thread raced the load and has already cached the image.
   if (images_.count(resource_id))
     return images_[resource_id];
 
   images_[resource_id] = image;
   return images_[resource_id];
 }
 
 }  // namespace ui