simplify element source lazy load

ext/fg/js/frame-offset-forwarder.js

@@ -94,27 +94,9 @@ class FrameOffsetForwarder {
     }
 
     _findFrameWithContentWindow(contentWindow) {
-        const elementSources = [
-            () => [...this._frameCache],
-            // will contain duplicates, but frame elements are cheap to handle
-            () => [...document.querySelectorAll('frame, iframe:not(.yomichan-float)')],
-            () => [document.documentElement]
-        ];
-        const getMoreElements = () => {
-            while (true) {
-                const source = elementSources.shift();
-                if (source) {
-                    const elements = source();
-                    if (elements.length === 0) { continue; }
-                    return elements;
-                }
-                return [];
-            }
-        };
-
-        const elements = [];
         const ELEMENT_NODE = Node.ELEMENT_NODE;
-        while (elements.length > 0 || elements.push(...getMoreElements())) {
+        for (const elements of this._getFrameElementSources()) {
+            while (elements.length > 0) {
                 const element = elements.shift();
                 if (element.contentWindow === contentWindow) {
                     this._frameCache.add(element);
@@ -136,10 +118,18 @@ class FrameOffsetForwarder {
                     }
                 }
             }
+        }
 
         return null;
     }
 
+    *_getFrameElementSources() {
+        yield [...this._frameCache];
+        // will contain duplicates, but frame elements are cheap to handle
+        yield [...document.querySelectorAll('frame, iframe:not(.yomichan-float)')];
+        yield [document.documentElement];
+    }
+
     _forwardFrameOffsetParent(offset, uniqueId) {
         window.parent.postMessage({action: 'getFrameOffset', params: {offset, uniqueId}}, '*');
     }