Log a message when microdump output is suppressed.

Change-Id: I11542ea9b702055e8f0b99c26cad2fea8681bce0
Reviewed-on: https://chromium-review.googlesource.com/417824
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Primiano Tucci <primiano@chromium.org>

src/client/linux/microdump_writer/microdump_writer.cc

@@ -166,6 +166,7 @@ class MicrodumpWriter {
   void Dump() {
     CaptureResult stack_capture_result = CaptureCrashingThreadStack(-1);
     if (stack_capture_result == CAPTURE_UNINTERESTING) {
+      LogLine("Microdump skipped (uninteresting)");
       return;
     }