fix and simplify

ext/fg/js/frontend.js

@@ -77,6 +77,7 @@ class Frontend extends TextScanner {
             chrome.runtime.onMessage.addListener(this.onRuntimeMessage.bind(this));
 
             this._updateContentScale();
+            this.popup.broadcastRootPopupInformation();
         } catch (e) {
             this.onError(e);
         }

ext/fg/js/popup-proxy.js

@@ -61,6 +61,10 @@ class PopupProxy {
         return true;
     }
 
+    broadcastRootPopupInformation() {
+        // NOP
+    }
+
     async setOptions(options) {
         const id = await this._getPopupId();
         return await this._invokeHostApi('setOptions', {id, options});
@@ -97,11 +101,11 @@ class PopupProxy {
 
     async showContent(elementRect, writingMode, type=null, details=null) {
         const id = await this._getPopupId();
-        let {x, y, width, height} = PopupProxy._convertDOMRectToJson(elementRect);
+        let {x, y, width, height} = elementRect;
         if (this._depth === 0) {
             [x, y] = await PopupProxy._convertIframePointToRootPagePoint(x, y);
-            elementRect = {x, y, width, height};
         }
+        elementRect = {x, y, width, height};
         return await this._invokeHostApi('showContent', {id, elementRect, writingMode, type, details});
     }
 
@@ -197,13 +201,4 @@ class PopupProxy {
 
         return offset;
     }
-
-    static _convertDOMRectToJson(domRect) {
-        return {
-            x: domRect.x,
-            y: domRect.y,
-            width: domRect.width,
-            height: domRect.height
-        };
-    }
 }

ext/fg/js/popup.js

@@ -199,8 +199,6 @@ class Popup {
     }
 
     async _createInjectPromise() {
-        this.broadcastRootPopupInformation();
-
         if (this._messageToken === null) {
             this._messageToken = await apiGetMessageToken();
         }