Fix lint error in TimelinePanel.js due to 'energy' variable.

Source/devtools/front_end/TimelinePanel.js

Index: Source/devtools/front_end/TimelinePanel.js
diff --git a/Source/devtools/front_end/TimelinePanel.js b/Source/devtools/front_end/TimelinePanel.js
index 79f10dfb6a07a22978696826f6ad27a2e9bc7b78..71fc05530a74916ff0cbe9bed06a2411dbc277d4 100644
--- a/Source/devtools/front_end/TimelinePanel.js
+++ b/Source/devtools/front_end/TimelinePanel.js
@@ -930,7 +930,7 @@ WebInspector.TimelinePanel.prototype = {
 
         if (Capabilities.canProfilePower) {
             var powerOverview = /** @type {!WebInspector.TimelinePowerOverview} */ (this._viewsForMode(WebInspector.TimelinePanel.Mode.Power).overviewView);
-            energy = powerOverview.calculateEnergy(startTime, endTime);
+            var energy = powerOverview.calculateEnergy(startTime, endTime);
             title += WebInspector.UIString("  Energy: %.2f Joules", energy);
         }
         this._detailsView.setContent(title, fragment);