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

base/android/content_uri_utils.cc

 // Copyright 2013 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 "base/android/content_uri_utils.h"
 
 #include "base/android/context_utils.h"
 #include "base/android/jni_android.h"
 #include "base/android/jni_string.h"
 #include "jni/ContentUriUtils_jni.h"
@@ skipping 25 matching lines @@
   return File(fd);
 }
 
 std::string GetContentUriMimeType(const FilePath& content_uri) {
   JNIEnv* env = base::android::AttachCurrentThread();
   ScopedJavaLocalRef<jstring> j_uri =
       ConvertUTF8ToJavaString(env, content_uri.value());
   ScopedJavaLocalRef<jstring> j_mime =
       Java_ContentUriUtils_getMimeType(
           env, base::android::GetApplicationContext(), j_uri.obj());
+  if (j_mime.is_null())
+    return std::string();
+
   return base::android::ConvertJavaStringToUTF8(env, j_mime.obj());
 }
 
 }  // namespace base