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

base/android/content_uri_utils.cc

Index: base/android/content_uri_utils.cc
diff --git a/base/android/content_uri_utils.cc b/base/android/content_uri_utils.cc
index 195598bfb3fd29dd03137bab7478aba8d750ed2c..31f7b4fffbf050f1500618bf7145a5285a09d45e 100644
--- a/base/android/content_uri_utils.cc
+++ b/base/android/content_uri_utils.cc
@@ -43,6 +43,9 @@ std::string GetContentUriMimeType(const FilePath& content_uri) {
   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());
 }