Fix MediaStorageUtil::CrackDeviceId function to include ":" in the media device type prefix.

chrome/browser/media_gallery/media_storage_util.cc

 // 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.
 
 // chrome::MediaStorageUtil implementation.
 
 #include "chrome/browser/media_gallery/media_storage_util.h"
 
 #include <vector>
 
@@ skipping 83 matching lines @@
       return std::string(kUsbMtpPrefix) + unique_id;
   }
   NOTREACHED();
   return std::string();
 }
 
 // static
 bool MediaStorageUtil::CrackDeviceId(const std::string& device_id,
                                      Type* type, std::string* unique_id) {
   size_t prefix_length = device_id.find_first_of(':');
-  std::string prefix = device_id.substr(0, prefix_length);
+  std::string prefix = prefix_length != std::string::npos ?
+                       device_id.substr(0, prefix_length + 1) : "";
 
   Type found_type;
   if (prefix == kUsbMassStorageWithDCIMPrefix) {
     found_type = USB_MASS_STORAGE_WITH_DCIM;
   } else if (prefix == kUsbMassStorageNoDCIMPrefix) {
     found_type = USB_MASS_STORAGE_NO_DCIM;
   } else if (prefix == kOtherMassStoragePrefix) {
     found_type = OTHER_MASS_STORAGE;
   } else if (prefix == kUsbMtpPrefix) {
     found_type = USB_MTP;
@@ skipping 108 matching lines @@
 void MediaStorageUtil::FindUSBDeviceById(const std::string& unique_id,
                                          const FilePathCallback& callback) {
   // TODO(vandebo) This needs to be implemented per platform.
   // Type is USB_MASS_STORAGE_NO_DCIM, so it's a device possibly mounted
   // somewhere...
   NOTREACHED();
   callback.Run(FilePath());
 }
 
 }  // namespace chrome