Bug 1358415: Don't trigger reflow just to compute tab geometry. r=aswan

MozReview-Commit-ID: DnFSbDfOskT

--HG--
extra : rebase_source : e6829657b250fa8ec893b3e73b7d9956dfe34424
extra : amend_source : f20cfab374b29b7d3475579a0fe5e11ab2e6dcb4

browser/components/extensions/ext-tabs.js

@@ -112,7 +112,7 @@ this.tabs = class extends ExtensionAPI {
 
         onCreated: new SingletonEventManager(context, "tabs.onCreated", fire => {
           let listener = (eventName, event) => {
-            fire.async(tabManager.convert(event.nativeTab));
+            fire.async(tabManager.convert(event.nativeTab, event.currentTab));
           };
 
           tabTracker.on("tab-created", listener);
@@ -360,6 +360,7 @@ this.tabs = class extends ExtensionAPI {
             options.disallowInheritPrincipal = true;
 
             tabListener.initTabReady();
+            let currentTab = window.gBrowser.selectedTab;
             let nativeTab = window.gBrowser.addTab(url || window.BROWSER_NEW_TAB_URL, options);
 
             let active = true;
@@ -394,7 +395,7 @@ this.tabs = class extends ExtensionAPI {
               tabListener.initializingTabs.add(nativeTab);
             }
 
-            return tabManager.convert(nativeTab);
+            return tabManager.convert(nativeTab, currentTab);
           });
         },
 

browser/components/extensions/ext-utils.js

@@ -238,13 +238,18 @@ class TabTracker extends TabTrackerBase {
           });
         }
 
+        // Save the current tab, since the newly-created tab will likely be
+        // active by the time the promise below resolves and the event is
+        // dispatched.
+        let currentTab = nativeTab.ownerGlobal.gBrowser.selectedTab;
+
         // We need to delay sending this event until the next tick, since the
         // tab does not have its final index when the TabOpen event is dispatched.
         Promise.resolve().then(() => {
           if (event.detail.adoptedTab) {
             this.emitAttached(event.originalTarget);
           } else {
-            this.emitCreated(event.originalTarget);
+            this.emitCreated(event.originalTarget, currentTab);
           }
         });
         break;
@@ -389,10 +394,12 @@ class TabTracker extends TabTrackerBase {
    *
    * @param {NativeTab} nativeTab
    *        The tab element which is being created.
+   * @param {NativeTab} [currentTab]
+   *        The tab element for the currently active tab.
    * @private
    */
-  emitCreated(nativeTab) {
-    this.emit("tab-created", {nativeTab});
+  emitCreated(nativeTab, currentTab) {
+    this.emit("tab-created", {nativeTab, currentTab});
   }
 
   /**
@@ -479,12 +486,18 @@ class Tab extends TabBase {
     return this.nativeTab.linkedBrowser;
   }
 
+  get frameLoader() {
+    // If we don't have a frameLoader yet, just return a dummy with no width and
+    // height.
+    return super.frameLoader || {lazyWidth: 0, lazyHeight: 0};
+  }
+
   get cookieStoreId() {
     return getCookieStoreIdForTab(this, this.nativeTab);
   }
 
   get height() {
-    return this.browser.clientHeight;
+    return this.frameLoader.lazyHeight;
   }
 
   get index() {
@@ -525,7 +538,7 @@ class Tab extends TabBase {
   }
 
   get width() {
-    return this.browser.clientWidth;
+    return this.frameLoader.lazyWidth;
   }
 
   get window() {

toolkit/components/extensions/ExtensionTabs.jsm

@@ -284,6 +284,15 @@ class TabBase {
     throw new Error("Not implemented");
   }
 
+  /**
+   * @property {nsIFrameLoader} browser
+   *        Returns the frameloader for the given tab.
+   *        @readonly
+   */
+  get frameLoader() {
+    return this.browser.frameLoader;
+  }
+
   /**
    * @property {string} cookieStoreId
    *        Returns the cookie store identifier for the given tab.
@@ -454,9 +463,12 @@ class TabBase {
    * of its properties which the extension is permitted to access, in the format
    * requried to be returned by WebExtension APIs.
    *
+   * @param {Tab} [fallbackTab]
+   *        A tab to retrieve geometry data from if the lazy geometry data for
+   *        this tab hasn't been initialized yet.
    * @returns {object}
    */
-  convert() {
+  convert(fallbackTab = null) {
     let result = {
       id: this.id,
       index: this.index,
@@ -472,6 +484,13 @@ class TabBase {
       mutedInfo: this.mutedInfo,
     };
 
+    // If the tab has not been fully layed-out yet, fallback to the geometry
+    // from a different tab (usually the currently active tab).
+    if (fallbackTab && (!result.width || !result.height)) {
+      result.width = fallbackTab.width;
+      result.height = fallbackTab.height;
+    }
+
     if (this.extension.hasPermission("cookies")) {
       result.cookieStoreId = this.cookieStoreId;
     }
@@ -1632,11 +1651,15 @@ class TabManagerBase {
    *
    * @param {NativeTab} nativeTab
    *        The native tab to convert.
+   * @param {NativeTab} [fallbackTab]
+   *        A tab to retrieve geometry data from if the lazy geometry data for
+   *        this tab hasn't been initialized yet.
    *
    * @returns {Object}
    */
-  convert(nativeTab) {
-    return this.getWrapper(nativeTab).convert();
+  convert(nativeTab, fallbackTab = null) {
+    return this.getWrapper(nativeTab)
+               .convert(fallbackTab && this.getWrapper(fallbackTab));
   }
 
   // The JSDoc validator does not support @returns tags in abstract functions or