Specific case for CBErrorMaxConnection in 10.12 or before

In enum CBError, for 10.13, CBErrorMaxConnection has been removed,
and CBErrorConnectionFailed and CBErrorConnectionLimitReached have
added.

10.12:
  * CBErrorMaxConnection (value 10): The device already has the
                                     maximum number of connections.
10.13:
  * CBErrorConnectionFailed (value 10): The connection failed.
  * CBErrorLimitReached (value 11): The device already has the
                                    maximum number of connections.
So for 10.12 or earlier, CBErrorMaxConnection should be counted as
CBERROR_CONNECTION_LIMIT_REACHED. 

Bug: 
Change-Id: I3f9dac126b5701639d7b5ed7984e414ddcc02d29
Reviewed-on: https://chromium-review.googlesource.com/680215
Commit-Queue: Jérôme Lebel <jlebel@chromium.org>
Reviewed-by: Vincent Scheib <scheib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504367}

device/bluetooth/bluetooth_adapter_mac_metrics.mm

@@ -7,6 +7,7 @@
 #import <CoreBluetooth/CoreBluetooth.h>
 #import <Foundation/Foundation.h>
 
+#include "base/mac/mac_util.h"
 #include "base/metrics/histogram_macros.h"
 
 namespace {
@@ -51,7 +52,15 @@ MacOSBluetoothOperationsResult GetMacOSOperationResultFromNSError(
       case CBErrorAlreadyAdvertising:
         return MacOSBluetoothOperationsResult::CBERROR_ALREADY_ADVERTISING;
       case CBErrorConnectionFailed:
-        return MacOSBluetoothOperationsResult::CBERROR_CONNECTION_FAILED;
+        if (base::mac::IsAtLeastOS10_13()) {
+          return MacOSBluetoothOperationsResult::CBERROR_CONNECTION_FAILED;
+        } else {
+          // For macOS 10.12 or before, the value CBErrorMaxConnection has the
+          // same value than CBErrorConnectionFailed and the same description
+          // than CBErrorConnectionLimitReached.
+          return MacOSBluetoothOperationsResult::
+              CBERROR_CONNECTION_LIMIT_REACHED;
+        }
       case CBErrorConnectionLimitReached:
         return MacOSBluetoothOperationsResult::CBERROR_CONNECTION_LIMIT_REACHED;
       case CBErrorUnkownDevice: