Bug 708746 - Part 3: Don't display a document until we've changed the browser size to match its viewport. r=kats

mobile/android/chrome/content/browser.js

@@ -163,11 +163,30 @@ var MetadataProvider = {
   },
 
   paintingSuppressed: function paintingSuppressed() {
-    let browser = BrowserApp.selectedBrowser;
+    // Get the current tab. Don't suppress painting if there are no tabs yet.
-    if (!browser)
+    let tab = BrowserApp.selectedTab;
+    if (!tab)
       return false;
-    let cwu = browser.contentWindow.QueryInterface(Ci.nsIInterfaceRequestor)
+
-                                   .getInterface(Ci.nsIDOMWindowUtils);
+    // If the viewport metadata has not yet been updated (and therefore the browser size has not
+    // been changed accordingly), do not draw yet. We'll get an unsightly flash on page transitions
+    // otherwise, because we receive a paint event after the new document is shown but before the
+    // correct browser size for the new document has been set.
+    //
+    // This whole situation exists because the docshell and the browser element are unaware of the
+    // existence of <meta viewport>. Therefore they dispatch paint events without knowledge of the
+    // invariant that the page must not be drawn until the browser size has been appropriately set.
+    // It would be easier if the docshell were made aware of the existence of <meta viewport> so
+    // that this logic could be removed.
+
+    let viewportDocumentId = tab.documentIdForCurrentViewport;
+    let contentDocumentId = ViewportHandler.getIdForDocument(tab.browser.contentDocument);
+    if (viewportDocumentId != null && viewportDocumentId != contentDocumentId)
+      return true;
+
+    // Suppress painting if the current presentation shell is suppressing painting.
+    let cwu = tab.browser.contentWindow.QueryInterface(Ci.nsIInterfaceRequestor)
+                                       .getInterface(Ci.nsIDOMWindowUtils);
     return cwu.paintingSuppressed;
   }
 };
@@ -1246,6 +1265,7 @@ function Tab(aURL, aParams) {
   this._viewport = { x: 0, y: 0, width: gScreenWidth, height: gScreenHeight, offsetX: 0, offsetY: 0,
                      pageWidth: gScreenWidth, pageHeight: gScreenHeight, zoom: 1.0 };
   this.viewportExcess = { x: 0, y: 0 };
+  this.documentIdForCurrentViewport = null;
   this.userScrollPos = { x: 0, y: 0 };
   this._pluginsToPlay = [];
   this._pluginOverlayShowing = false;
@@ -1302,8 +1322,10 @@ Tab.prototype = {
     this.browser.addEventListener("scroll", this, true);
     this.browser.addEventListener("PluginClickToPlay", this, true);
     this.browser.addEventListener("pagehide", this, true);
+    this.browser.addEventListener("pageshow", this, true);
 
     Services.obs.addObserver(this, "http-on-modify-request", false);
+    Services.obs.addObserver(this, "document-shown", false);
 
     if (!aParams.delayLoad) {
       let flags = "flags" in aParams ? aParams.flags : Ci.nsIWebNavigation.LOAD_FLAGS_NONE;
@@ -1363,6 +1385,7 @@ Tab.prototype = {
     this.browser.removeEventListener("scroll", this, true);
     this.browser.removeEventListener("PluginClickToPlay", this, true);
     this.browser.removeEventListener("pagehide", this, true);
+    this.browser.removeEventListener("pageshow", this, true);
 
     // Make sure the previously selected panel remains selected. The selected panel of a deck is
     // not stable when panels are removed.
@@ -1373,6 +1396,7 @@ Tab.prototype = {
     Services.obs.removeObserver(this, "http-on-modify-request", false);
     this.browser = null;
     this.vbox = null;
+    this.documentIdForCurrentViewport = null;
     let message = {
       gecko: {
         type: "Tab:Closed",
@@ -1529,8 +1553,6 @@ Tab.prototype = {
         if (target.defaultView != this.browser.contentWindow)
           return;
 
-        this.updateViewport(true);
-
         sendMessageToJava({
           gecko: {
             type: "DOMContentLoaded",
@@ -1924,18 +1946,31 @@ Tab.prototype = {
   },
 
   observe: function(aSubject, aTopic, aData) {
-    if (!(aSubject instanceof Ci.nsIHttpChannel))
+    switch (aTopic) {
-      return;
+      case "http-on-modify-request":
+        if (!(aSubject instanceof Ci.nsIHttpChannel))
+          return;
 
-    let channel = aSubject.QueryInterface(Ci.nsIHttpChannel);
+        let channel = aSubject.QueryInterface(Ci.nsIHttpChannel);
-    if (!(channel.loadFlags & Ci.nsIChannel.LOAD_DOCUMENT_URI))
+        if (!(channel.loadFlags & Ci.nsIChannel.LOAD_DOCUMENT_URI))
-      return;
+          return;
 
-    let channelWindow = this.getWindowForRequest(channel);
+        let channelWindow = this.getWindowForRequest(channel);
-    if (channelWindow == this.browser.contentWindow) {
+        if (channelWindow == this.browser.contentWindow) {
-      this.setHostFromURL(channel.URI.spec);
+          this.setHostFromURL(channel.URI.spec);
-      if (this.agentMode == UA_MODE_DESKTOP)
+          if (this.agentMode == UA_MODE_DESKTOP)
-        channel.setRequestHeader("User-Agent", "Mozilla/5.0 (X11; Linux x86_64; rv:7.0.1) Gecko/20100101 Firefox/7.0.1", false);
+            channel.setRequestHeader("User-Agent", "Mozilla/5.0 (X11; Linux x86_64; rv:7.0.1) Gecko/20100101 Firefox/7.0.1", false);
+        }
+        break;
+
+      case "document-shown":
+        // Is it on the top level?
+        let contentDocument = aSubject;
+        if (contentDocument == this.browser.contentDocument) {
+          ViewportHandler.updateMetadata(this);
+          this.documentIdForCurrentViewport = ViewportHandler.getIdForDocument(contentDocument);
+        }
+        break;
     }
   },
 
@@ -2828,6 +2863,11 @@ var ViewportHandler = {
   // ES6 weak map lets us avoid leaks.
   _metadata: new WeakMap(),
 
+  // A list of document IDs, arbitrarily assigned. We use IDs to refer to content documents instead
+  // of strong references to avoid leaking them.
+  _documentIds: new WeakMap(),
+  _nextDocumentId: 0,
+
   init: function init() {
     addEventListener("DOMWindowCreated", this, false);
     addEventListener("DOMMetaAdded", this, false);
@@ -3001,6 +3041,19 @@ var ViewportHandler = {
       autoScale: true,
       scaleRatio: ViewportHandler.getScaleRatio()
     };
+  },
+
+  /**
+   * Returns a globally unique ID for the given content document. Using IDs to refer to documents
+   * allows content documents to be identified without any possibility of leaking them.
+   */
+  getIdForDocument: function getIdForDocument(aDocument) {
+    let id = this._documentIds.get(aDocument, null);
+    if (id == null) {
+      id = this._nextDocumentId++;
+      this._documentIds.set(aDocument, id);
+    }
+    return id;
   }
 };