DCHECK that jstring to C++ string conversions don't pass in null.

components/gcm_driver/gcm_driver_android.cc

 // Copyright 2014 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 "components/gcm_driver/gcm_driver_android.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "base/android/context_utils.h"
@@ skipping 66 matching lines @@
     const JavaParamRef<jstring>& j_sender_id,
     const JavaParamRef<jstring>& j_collapse_key,
     const JavaParamRef<jbyteArray>& j_raw_data,
     const JavaParamRef<jobjectArray>& j_data_keys_and_values) {
   std::string app_id = ConvertJavaStringToUTF8(env, j_app_id);
 
   int message_byte_size = 0;
 
   IncomingMessage message;
   message.sender_id = ConvertJavaStringToUTF8(env, j_sender_id);
-  message.collapse_key = ConvertJavaStringToUTF8(env, j_collapse_key);
+  if (!j_collapse_key.is_null())
+    ConvertJavaStringToUTF8(env, j_collapse_key, &message.collapse_key);
+
   // Expand j_data_keys_and_values from array to map.
   std::vector<std::string> data_keys_and_values;
   AppendJavaStringArrayToStringVector(env,
                                       j_data_keys_and_values,
                                       &data_keys_and_values);
   for (size_t i = 0; i + 1 < data_keys_and_values.size(); i += 2) {
     message.data[data_keys_and_values[i]] = data_keys_and_values[i+1];
     message_byte_size += data_keys_and_values[i+1].size();
   }
   // Convert j_raw_data from byte[] to binary std::string.
@@ skipping 159 matching lines @@
   NOTIMPLEMENTED();
 }
 
 void GCMDriverAndroid::RecordDecryptionFailure(
     const std::string& app_id,
     GCMEncryptionProvider::DecryptionResult result) {
   recorder_.RecordDecryptionFailure(app_id, result);
 }
 
 }  // namespace gcm