Runtime checks so that CoreBluetooth only used on >= 10.10

device/bluetooth/bluetooth_adapter_mac_unittest.mm

Index: device/bluetooth/bluetooth_adapter_mac_unittest.mm
diff --git a/device/bluetooth/bluetooth_adapter_mac_unittest.mm b/device/bluetooth/bluetooth_adapter_mac_unittest.mm
index 3e7ab6832ede2641ba91284e7597cdc009d3560b..8e0024b788b032b53bd5459b6a6086fb42fb0539 100644
--- a/device/bluetooth/bluetooth_adapter_mac_unittest.mm
+++ b/device/bluetooth/bluetooth_adapter_mac_unittest.mm
@@ -25,9 +25,10 @@ class BluetoothAdapterMacTest : public testing::Test {
 
   // Helper methods for setup and access to BluetoothAdapterMacTest's members.
   bool SetMockCentralManager() {
-    Class aClass = NSClassFromString(@"CBCentralManager");
-    if (aClass == nil) {
-      LOG(WARNING) << "CoreBluetooth not available, skipping unit test.";
+    if (!BluetoothAdapterMac::IsLowEnergyAvailable()) {
+      // For stability we only use CoreBluetooth on OS X >= 10.10.  Thus on
+      // previous OS X versions the code cannot be tested.
+      LOG(WARNING) << "OS X version < 10.10, skipping unit test.";
       return false;
     }
     mock_central_manager_ = [[MockCentralManager alloc] init];