Bail out when counting hidden elements is too expensive

Related issue:
- https://github.com/uBlockOrigin/uBlock-issues/issues/756

When trying the number of hidden elements as a result of
cosmetic filtering for popup panel badge purpose, the
code will bail out if this takes too long, and in such
case the badge will be set to `?`, meaning the number
of hidden elements is undetermined.

src/js/messaging.js

@@ -374,10 +374,11 @@ const getElementCount = async function(tabId, what) {
     });
 
     let total = 0;
-    results.forEach(count => {
-        if ( typeof count !== 'number' ) { return; }
+    for ( const count of results ) {
+        if ( typeof count !== 'number' ) { continue; }
+        if ( count === -1 ) { return -1; }
         total += count;
-    });
+    }
 
     return total;
 };

src/js/popup.js

@@ -688,9 +688,15 @@ const renderPopupLazy = (( ) => {
                 what: 'getHiddenElementCount',
                 tabId: popupData.tabId,
             }).then(count => {
-                badge.textContent = (count || 0) !== 0
-                    ? Math.min(count, 99).toLocaleString()
-                    : '';
+                let text;
+                if ( (count || 0) === 0 ) {
+                    text = '';
+                } else if ( count === -1 ) {
+                    text = '?';
+                } else {
+                    text = Math.min(count, 99).toLocaleString();
+                }
+                badge.textContent = text;
                 sw.classList.remove('hnSwitchBusy');
             });
         };

src/js/scriptlets/dom-survey-elements.js

@@ -30,11 +30,12 @@
     if ( typeof vAPI !== 'object' ) { return; }
 
     const t0 = Date.now();
+    const tMax = t0 + 100;
 
     if ( vAPI.domSurveyElements instanceof Object === false ) {
         vAPI.domSurveyElements = {
             busy: false,
-            hiddenElementCount: -1,
+            hiddenElementCount: Number.NaN,
             surveyTime: t0,
         };
     }
@@ -44,11 +45,11 @@
     surveyResults.busy = true;
 
     if ( surveyResults.surveyTime < vAPI.domMutationTime ) {
-        surveyResults.hiddenElementCount = -1;
+        surveyResults.hiddenElementCount = Number.NaN;
     }
     surveyResults.surveyTime = t0;
 
-    if ( surveyResults.hiddenElementCount === -1 ) {
+    if ( isNaN(surveyResults.hiddenElementCount) ) {
         surveyResults.hiddenElementCount = (( ) => {
             if ( vAPI.domFilterer instanceof Object === false ) { return 0; }
             const details = vAPI.domFilterer.getAllSelectors_(true);
@@ -90,6 +91,7 @@
                     candidates.delete(node);
                     matched.add(node);
                     if ( matched.size === 99 ) { break; }
+                    if ( Date.now() > tMax ) { return -1; }
                 }
             }
             if ( matched.size < 99 && complexStr !== '') {
@@ -97,6 +99,7 @@
                     if ( node.closest(complexStr) !== node ) { continue; }
                     matched.add(node);
                     if ( matched.size === 99 ) { break; }
+                    if ( Date.now() > tMax ) { return -1; }
                 }
             }
             return matched.size;