Improves UMA stat related to built-in AGC monitoring on iOS

modules/audio_device/ios/voice_processing_audio_unit.mm

 /*
  *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 235 matching lines @@
   }
   if (result == noErr) {
     RTCLog(@"Voice Processing I/O unit is now initialized.");
   }
 
   // AGC should be enabled by default for Voice Processing I/O units but it is
   // checked below and enabled explicitly if needed. This scheme is used
   // to be absolutely sure that the AGC is enabled since we have seen cases
   // where only zeros are recorded and a disabled AGC could be one of the
   // reasons why it happens.
-  int agc_was_enabled_by_default = 1;
+  int agc_was_enabled_by_default = 0;
   UInt32 agc_is_enabled = 0;
   result = GetAGCState(vpio_unit_, &agc_is_enabled);
   if (result != noErr) {
     RTCLogError(@"Failed to get AGC state (1st attempt). "
                  "Error=%ld.",
                 (long)result);
-  } else if (!agc_is_enabled) {
-    // Remember that the AGC was disabled by default. Will be used in UMA.
-    agc_was_enabled_by_default = 0;
-    // Try to enable the AGC.
+    UMA_HISTOGRAM_SPARSE_SLOWLY("WebRTC.Audio.GetAGCStateErrorCode", result);
+  } else if (agc_is_enabled) {
+    // Remember that the AGC was enabled by default. Will be used in UMA.
+    agc_was_enabled_by_default = 1;
+  } else {
+    // AGC was initially disabled => try to enable it explicitly.
     UInt32 enable_agc = 1;
     result =
         AudioUnitSetProperty(vpio_unit_,
                              kAUVoiceIOProperty_VoiceProcessingEnableAGC,
                              kAudioUnitScope_Global, kInputBus, &enable_agc,
                              sizeof(enable_agc));
     if (result != noErr) {
       RTCLogError(@"Failed to enable the built-in AGC. "
                    "Error=%ld.",
                   (long)result);
+      UMA_HISTOGRAM_SPARSE_SLOWLY("WebRTC.Audio.SetAGCStateErrorCode", result);
     }
     result = GetAGCState(vpio_unit_, &agc_is_enabled);
     if (result != noErr) {
       RTCLogError(@"Failed to get AGC state (2nd attempt). "
                    "Error=%ld.",
                   (long)result);
+      // Use same histogram as earlier but multiply error code with -1 to
+      // make each case unique. Example: kAudioUnitErr_NoConnection (-10876)
+      // will be converted to +10876 here.
+      UMA_HISTOGRAM_SPARSE_SLOWLY(
+          "WebRTC.Audio.GetAGCStateErrorCode", (-1) * result);
     }
   }
 
   // Track if the built-in AGC was enabled by default (as it should) or not.
   RTC_HISTOGRAM_BOOLEAN("WebRTC.Audio.BuiltInAGCWasEnabledByDefault",
                         agc_was_enabled_by_default);
   RTCLog(@"WebRTC.Audio.BuiltInAGCWasEnabledByDefault: %d",
          agc_was_enabled_by_default);
   // As a final step, add an UMA histogram for tracking the AGC state.
   // At this stage, the AGC should be enabled, and if it is not, more work is
@@ skipping 155 matching lines @@
     OSStatus result = AudioComponentInstanceDispose(vpio_unit_);
     if (result != noErr) {
       RTCLogError(@"AudioComponentInstanceDispose failed. Error=%ld.",
                   (long)result);
     }
     vpio_unit_ = nullptr;
   }
 }
 
 }  // namespace webrtc