Don't spawn an upload thread if url is empty

Also automatically stop upload and prune threads on destruction.

Bug: crashpad:30
Change-Id: I45a30944eb3052182da296e00a6d6041691ab772
Reviewed-on: https://chromium-review.googlesource.com/924456
Commit-Queue: Joshua Peraza <[email protected]>
Reviewed-by: Mark Mentovai <[email protected]>
diff --git a/handler/mac/crash_report_exception_handler.h b/handler/mac/crash_report_exception_handler.h
index cc314f1..0b44de6 100644
--- a/handler/mac/crash_report_exception_handler.h
+++ b/handler/mac/crash_report_exception_handler.h
@@ -36,7 +36,8 @@
   //!
   //! \param[in] database The database to store crash reports in. Weak.
   //! \param[in] upload_thread The upload thread to notify when a new crash
-  //!     report is written into \a database.
+  //!     report is written into \a database. Report upload is skipped if this
+  //!     value is `nullptr`.
   //! \param[in] process_annotations A map of annotations to insert as
   //!     process-level annotations into each crash report that is written. Do
   //!     not confuse this with module-level annotations, which are under the