Expose TxPower for bluetooth devices during discovery

extensions/common/api/bluetooth.idl

Index: extensions/common/api/bluetooth.idl
diff --git a/extensions/common/api/bluetooth.idl b/extensions/common/api/bluetooth.idl
index 9051289e6596198e0ab2be25eb2494103b97710a..98908f06b7a0badf0c15553c313cc13dd3cb3a79 100644
--- a/extensions/common/api/bluetooth.idl
+++ b/extensions/common/api/bluetooth.idl
@@ -75,6 +75,11 @@ namespace bluetooth {
     // The received signal strength, in dBm. This field is avaliable and valid
     // only during discovery. Outside of discovery it's value is not specified.
     long? inquiryRssi;
+  
+    // The transmitted power level. This field is avaliable only for LE devices
+    // that include this field in AD. It is avaliable and valid only during
+    // discovery.
+    long? inquiryTxPower;
   };
 
   // Callback from the <code>getDevice</code> method.