Update components/profile/trace-dump.js to 6f7906

This updates the trace-dump.js file to
fitzgen/servo-trace-dump@6f79066:

> commit 6f790668140d44a8641e441d3ac0e64364b8c0ca
> Author: Nick Fitzgerald <fitzgen@gmail.com>
> Date:   Fri Mar 31 14:26:31 2017 -0700
>
>     Update for new serde-json data format
>
>     Not sure when this happened, but at some point enum variants without any tuple
>     struct members became simple strings.

components/profile/trace-dump.js

@@ -244,11 +244,6 @@ Make sure to upstream changes, or they will get lost!
     return increment;
   };
 
-  // Get the category name for the given trace.
-  const traceCategory = exports.traceCategory = trace => {
-    return Object.keys(trace.category)[0];
-  };
-
   /*** Window Specific Code ***************************************************/
 
   if (!window) {
@@ -528,7 +523,7 @@ Make sure to upstream changes, or they will get lost!
     inner.style.width = state.nsToSelectionPx(trace.endTime - trace.startTime) + "px";
     inner.style.marginLeft = state.nsToSelectionPx(trace.startTime - state.startSelection) + "px";
 
-    let category = traceCategory(trace);
+    let category = trace.category;
     inner.textContent = category;
     inner.style.backgroundColor = state.getColorForCategory(category);