Fix uninitialized variable in test

Callback should set result if it returned true.
Detected with "init_stack_vars = true".

Bug: 1030261
Change-Id: I9088a0ab498c44f9a765bf89361c91298d9458e8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1949643Reviewed-by: Albert J. Wong <ajwong@chromium.org>
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#721291}

base/message_loop/message_loop_unittest.cc

@@ -1565,6 +1565,7 @@ bool QuitOnSystemTimer(UINT message,
     ThreadTaskRunnerHandle::Get()->PostTask(FROM_HERE,
                                             BindOnce(&::PostQuitMessage, 0));
   }
+  *result = 0;
   return true;
 }
 
@@ -1579,6 +1580,7 @@ bool DelayedQuitOnSystemTimer(UINT message,
         FROM_HERE, BindOnce(&::PostQuitMessage, 0),
         TimeDelta::FromMilliseconds(10));
   }
+  *result = 0;
   return true;
 }