Change the 'is-ready' message after profiler changed its postMessage API (#8)

This is changed in firefox-devtools/profiler#5148.
Previously we were using 'is-ready' for both the request and the
response. Now we are using two distinct messages on both for clarity.

Author: canova

index.html

@@ -359,7 +359,7 @@ <h1 id="power"><span id="deviceNameH1">USB</span> live profile: <span id="lastPo
 
       let isReady = false;
       window.addEventListener("message", function listener(event) {
-        if (event.data && event.data.name === "is-ready") {
+        if (event.data && event.data.name === "ready:response") {
           window.removeEventListener("message", listener);
           isReady = true;
           const message = {
@@ -375,7 +375,7 @@ <h1 id="power"><span id="deviceNameH1">USB</span> live profile: <span id="lastPo
         if (isReady) {
           break;
         }
-        profilerWindow.postMessage({ name: "is-ready" }, origin);
+        profilerWindow.postMessage({ name: "ready:request" }, origin);
       }
     }