[resultsdbpy] Add "no results" message for when no test results are r…

…eturned from the server.

rdar://113864624
https://bugs.webkit.org/show_bug.cgi?id=260162

Reviewed by Jonathan Bedard.

Adds/demystifies UI feedback for no build results found for existing test.

* Tools/Scripts/libraries/resultsdbpy/resultsdbpy/view/static/js/timeline.js:
(TimelineFromEndpoint.prototype.reload):

Canonical link: https://commits.webkit.org/266916@main

Tools/Scripts/libraries/resultsdbpy/resultsdbpy/view/static/js/timeline.js

@@ -464,6 +464,13 @@ class TimelineFromEndpoint {
                 response.json().then(json => {
                     if (myDispatch !== this.latestDispatch)
                         return;
+                    else if (json.length === 0) {
+                        this.ref.setState({
+                            error: "No results found for the requested test under the selected configuration.",
+                            description: "This could be because the selected configuration is not tested (check test expectations), no builds were completed, or the test does not exist."
+                        });
+                        return;
+                    }
 
                     let oldestUuid = Date.now() / 10;
                     let newestUuid = 0;