[Telemetry] Stop refreshing on destroy

Stop polling for updates to telemetry data from
TelemetryController when scope is destroyed.
Addresses some performance issues observed in
WTD-614, autoflow tabular views (although this
view doesn't use TelemetryController directly,
the continuing of this polling in the background
can slow down updates when it is showing.)

platform/telemetry/src/TelemetryController.js

@@ -49,7 +49,11 @@ define(
 
                 // Used for getTelemetryObjects; a reference is
                 // stored so that this can be called in a watch
-                telemetryObjects: []
+                telemetryObjects: [],
+
+                // Whether or not this controller is active; once
+                // scope is destroyed, polling should stop.
+                active: true
             };
 
             // Broadcast that a telemetryUpdate has occurred.
@@ -227,14 +231,25 @@ define(
                         }
 
                         self.refreshing = false;
+
+                        if (self.active) {
                             startTimeout();
+                        }
                     }, self.interval);
                 }
             }
 
+            // Stop polling for changes
+            function deactivate() {
+                self.active = false;
+            }
+
             // Watch for a represented domain object
             $scope.$watch("domainObject", getTelemetryObjects);
 
+            // Stop polling when destroyed
+            $scope.$on("$destroy", deactivate);
+
             // Begin polling for data changes
             startTimeout();