Bug 1002426 - Check restore status before overriding zoom. r=kats

dom/base/nsDOMWindowUtils.cpp

@@ -576,6 +576,23 @@ nsDOMWindowUtils::GetResolution(float* aXResolution, float* aYResolution)
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsDOMWindowUtils::GetIsHistoryRestored(bool* aIsHistoryRestored) {
+  if (!nsContentUtils::IsCallerChrome()) {
+    return NS_ERROR_DOM_SECURITY_ERR;
+  }
+
+  nsIPresShell* presShell = GetPresShell();
+  if (!presShell) {
+    return NS_ERROR_FAILURE;
+  }
+
+  const nsIScrollableFrame* sf = presShell->GetRootScrollFrameAsScrollable();
+  *aIsHistoryRestored = sf && sf->DidHistoryRestore();
+
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 nsDOMWindowUtils::SetIsFirstPaint(bool aIsFirstPaint)
 {

dom/interfaces/base/nsIDOMWindowUtils.idl

@@ -48,7 +48,7 @@ interface nsIRunnable;
 interface nsICompositionStringSynthesizer;
 interface nsITranslationNodeList;
 
-[scriptable, uuid(d68ea9fa-b1ea-4744-a78e-bb0e6ef95f55)]
+[scriptable, uuid(8489681a-7407-457e-b889-53d1ae999b30)]
 interface nsIDOMWindowUtils : nsISupports {
 
   /**
@@ -230,6 +230,15 @@ interface nsIDOMWindowUtils : nsISupports {
 
   void getResolution(out float aXResolution, out float aYResolution);
 
+  /**
+   * Whether the current window has been restored from session history.
+   * This gives a way to check whether the provided resolution and scroll
+   * position are default values or restored from a previous session.
+   *
+   * Can only be accessed with chrome privileges.
+   */
+  readonly attribute boolean isHistoryRestored;
+
   /**
    * Whether the next paint should be flagged as the first paint for a document.
    * This gives a way to track the next paint that occurs after the flag is

layout/generic/nsGfxScrollFrame.h

@@ -658,7 +658,7 @@ public:
   virtual void ResetScrollPositionForLayerPixelAlignment() MOZ_OVERRIDE {
     mHelper.ResetScrollPositionForLayerPixelAlignment();
   }
-  virtual bool DidHistoryRestore() MOZ_OVERRIDE {
+  virtual bool DidHistoryRestore() const MOZ_OVERRIDE {
     return mHelper.mDidHistoryRestore;
   }
   virtual void ClearDidHistoryRestore() MOZ_OVERRIDE {
@@ -972,7 +972,7 @@ public:
   virtual void ResetScrollPositionForLayerPixelAlignment() MOZ_OVERRIDE {
     mHelper.ResetScrollPositionForLayerPixelAlignment();
   }
-  virtual bool DidHistoryRestore() MOZ_OVERRIDE {
+  virtual bool DidHistoryRestore() const MOZ_OVERRIDE {
     return mHelper.mDidHistoryRestore;
   }
   virtual void ClearDidHistoryRestore() MOZ_OVERRIDE {

layout/generic/nsIScrollableFrame.h

@@ -270,7 +270,7 @@ public:
   /**
    * Was the current presentation state for this frame restored from history?
    */
-  virtual bool DidHistoryRestore() = 0;
+  virtual bool DidHistoryRestore() const = 0;
   /**
    * Clear the flag so that DidHistoryRestore() returns false until the next
    * RestoreState call.

mobile/android/chrome/content/browser.js

@@ -4204,20 +4204,26 @@ Tab.prototype = {
     sendMessageToJava(message);
   },
 
+  _getGeckoZoom: function() {
+    let res = {x: {}, y: {}};
+    let cwu = this.browser.contentWindow.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
+    cwu.getResolution(res.x, res.y);
+    let zoom = res.x.value * window.devicePixelRatio;
+    return zoom;
+  },
+
   saveSessionZoom: function(aZoom) {
     let cwu = this.browser.contentWindow.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
     cwu.setResolution(aZoom / window.devicePixelRatio, aZoom / window.devicePixelRatio);
   },
 
   restoredSessionZoom: function() {
-    if (!this._restoreZoom) {
-      return null;
-    }
-
     let cwu = this.browser.contentWindow.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils);
-    let res = {x: {}, y: {}};
-    cwu.getResolution(res.x, res.y);
-    return res.x.value * window.devicePixelRatio;
+
+    if (this._restoreZoom && cwu.isHistoryRestored) {
+      return this._getGeckoZoom();
+    }
+    return null;
   },
 
   OnHistoryNewEntry: function(aUri) {