Sensor.start(): Check for permission before attempting to connect to sensor.

This better reflects the current implementation in Chromium. Additionally,
it makes more sense to check for permission and bail out early than to run
"connect to sensor", failing and having to remove the connection.

Author: Raphael Kubo da Costa

index.bs

@@ -1145,6 +1145,13 @@ It represents a [=reading timestamp=].
         return.
     1.  Set [=this=].{{[[state]]}} to "activating".
     1.  Run these sub-steps [=in parallel=]:
+        1.  Let |permissionState| be the result of invoking
+            [=request sensor access=] with [=this=] as argument.
+        1.  If |permissionState| is "denied", then:
+            1.  Let |e| be the result of [=created|creating=]
+                a "{{NotAllowedError!!exception}}" {{DOMException}}.
+            1.  Queue a task to run [=notify error=] with [=this=] and |e| as arguments.
+            1.  Return.
         1.  Let |connected| be the result of invoking [=connect to sensor=] with [=this=]
             as argument.
         1.  If |connected| is false, then
@@ -1162,14 +1169,7 @@ It represents a [=reading timestamp=].
                 but it is a tradeoff some User Agent might choose to make. -->
             1.  Queue a task to run [=notify error=] with [=this=] and |e| as arguments.
             1.  Return.
-        1.  Let |permission_state| be the result of invoking
-            [=request sensor access=] with [=this=] as argument.
-        1.  If |permission_state| is "granted",
-            1.  Invoke [=activate a sensor object=] with [=this=] as argument.
-        1.  Otherwise, if |permission_state| is "denied",
-            1.  Let |e| be the result of [=created|creating=]
-                a "{{NotAllowedError!!exception}}" {{DOMException}}.
-            1.  Queue a task to run [=notify error=] with [=this=] and |e| as arguments.
+        1.  Invoke [=activate a sensor object=] with [=this=] as argument.
 </div>