[resultsdb] rewrite JS unexpectedResults for clarity

https://bugs.webkit.org/show_bug.cgi?id=270448
rdar://problem/124013364

Reviewed by Jonathan Bedard.

Based on profiling in both Safari and Chrome, this doesn't meaningfully
change the performance of the hot code. In either browser,
unexpectedResults scarcely manages to get sampled.

* Tools/Scripts/libraries/resultsdbpy/resultsdbpy/view/static/js/expectations.js:
(Expectations.unexpectedResults):

Canonical link: https://commits.webkit.org/275628@main

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

@@ -56,23 +56,22 @@ class Expectations
 
     static unexpectedResults(results, expectations)
     {
-        let r = results.split('.');
-        expectations.split(' ').forEach(expectation => {
-            const i = r.indexOf(expectation);
-            if (i > -1)
-                r.splice(i, 1);
-            if (expectation === 'FAIL')
-                ['TEXT', 'AUDIO', 'IMAGE'].forEach(expectation => {
-                    const i = r.indexOf(expectation);
-                    if (i > -1)
-                        r.splice(i, 1);
-                });
-        });
+        const unexpectedSet = new Set(results.split('.'));
+        const expectedSet = new Set(expectations.split(' '));
+
+        if (expectedSet.has('FAIL'))
+            expectedSet.add('TEXT').add('AUDIO').add('IMAGE');
+
+        for (const result of unexpectedSet) {
+            if (expectedSet.has(result))
+                unexpectedSet.delete(result);
+        }
+
         let result = 'PASS';
-        r.forEach(candidate => {
+        for (const candidate of unexpectedSet) {
             if (Expectations.stringToStateId(candidate) < Expectations.stringToStateId(result))
                 result = candidate;
-        });
+        }
         return result;
     }
 }