Fixes bug in Media.AudioInputCbErrorMac histogram.

We are trying to track down a negative error code (-50) but the current implementation logs negative values as zero. This patch maps all -50 error codes into one bin and all other error values into a second (unspecified/trash) bin.

BUG=428706

Review URL: https://codereview.chromium.org/702453003

Cr-Commit-Position: refs/heads/master@{#302434}

media/audio/mac/audio_low_latency_input_mac.cc

@@ -9,7 +9,7 @@
 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/mac/mac_logging.h"
-#include "base/metrics/histogram.h"
+#include "base/metrics/sparse_histogram.h"
 #include "media/audio/mac/audio_manager_mac.h"
 #include "media/base/audio_bus.h"
 #include "media/base/data_buffer.h"
@@ -498,7 +498,7 @@ OSStatus AUAudioInputStream::InputProc(void* user_data,
                                     number_of_frames,
                                     audio_input->audio_buffer_list());
   if (result) {
-    UMA_HISTOGRAM_COUNTS("Media.AudioInputCbErrorMac", result);
+    UMA_HISTOGRAM_SPARSE_SLOWLY("Media.AudioInputCbErrorMac", result);
     NOTREACHED();
     return result;
   }