Bug 1169512 - Add and remove quirk.css rather than enable and disable a clone of it. r=jwatt

layout/base/nsDocumentViewer.cpp

@@ -2298,22 +2298,6 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument,
       styleSet->PrependStyleSheet(nsStyleSet::eAgentSheet, sheet);
     }
 
-    // Make sure to clone the quirk sheet so that it can be usefully
-    // enabled/disabled as needed.
-    nsRefPtr<CSSStyleSheet> quirkClone;
-    CSSStyleSheet* quirkSheet;
-    if (!nsLayoutStylesheetCache::UASheet() ||
-        !(quirkSheet = nsLayoutStylesheetCache::QuirkSheet()) ||
-        !(quirkClone = quirkSheet->Clone(nullptr, nullptr, nullptr, nullptr)) ||
-        !sheet) {
-      delete styleSet;
-      return NS_ERROR_OUT_OF_MEMORY;
-    }
-    // quirk.css needs to come after the regular UA sheet (or more precisely,
-    // after the html.css and so forth that the UA sheet imports).
-    styleSet->PrependStyleSheet(nsStyleSet::eAgentSheet, quirkClone);
-    styleSet->SetQuirkStyleSheet(quirkClone);
-
     if (aDocument->LoadsFullXULStyleSheetUpFront()) {
       // nsXULElement::BindToTree loads xul.css on-demand if we don't load it
       // up-front here.
@@ -2349,6 +2333,9 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument,
       }
     }
 
+    // We don't add quirk.css here; nsPresContext::CompatibilityModeChanged will
+    // append it if needed.
+
     sheet = nsLayoutStylesheetCache::HTMLSheet();
     if (sheet) {
       styleSet->PrependStyleSheet(nsStyleSet::eAgentSheet, sheet);

layout/base/nsPresContext.cpp

@@ -1354,12 +1354,40 @@ nsPresContext::GetDisplayRootPresContext()
 void
 nsPresContext::CompatibilityModeChanged()
 {
-  if (!mShell)
+  if (!mShell) {
     return;
+  }
 
-  // enable/disable the QuirkSheet
-  mShell->StyleSet()->
-    EnableQuirkStyleSheet(CompatibilityMode() == eCompatibility_NavQuirks);
+  nsIDocument* doc = mShell->GetDocument();
+  if (!doc) {
+    return;
+  }
+
+  if (doc->IsSVGDocument()) {
+    // SVG documents never load quirk.css.
+    return;
+  }
+
+  bool needsQuirkSheet = CompatibilityMode() == eCompatibility_NavQuirks;
+  if (mQuirkSheetAdded == needsQuirkSheet) {
+    return;
+  }
+
+  nsStyleSet* styleSet = mShell->StyleSet();
+  CSSStyleSheet* sheet = nsLayoutStylesheetCache::QuirkSheet();
+
+  if (needsQuirkSheet) {
+    // quirk.css needs to come after html.css; we just keep it at the end.
+    DebugOnly<nsresult> rv =
+      styleSet->AppendStyleSheet(nsStyleSet::eAgentSheet, sheet);
+    NS_WARN_IF_FALSE(NS_SUCCEEDED(rv), "failed to insert quirk.css");
+  } else {
+    DebugOnly<nsresult> rv =
+      styleSet->RemoveStyleSheet(nsStyleSet::eAgentSheet, sheet);
+    NS_WARN_IF_FALSE(NS_SUCCEEDED(rv), "failed to remove quirk.css");
+  }
+
+  mQuirkSheetAdded = needsQuirkSheet;
 }
 
 // Helper function for setting Anim Mode on image

layout/base/nsPresContext.h

@@ -1399,6 +1399,9 @@ protected:
 
   unsigned mHasWarnedAboutPositionedTableParts : 1;
 
+  // Have we added quirk.css to the style set?
+  unsigned              mQuirkSheetAdded : 1;
+
 #ifdef RESTYLE_LOGGING
   // Should we output debug information about restyling for this document?
   bool                  mRestyleLoggingEnabled;

layout/style/nsCSSRuleProcessor.h

@@ -161,13 +161,6 @@ public:
    */
   mozilla::dom::Element* GetScopeElement() const { return mScopeElement; }
 
-#ifdef DEBUG
-  void AssertQuirksChangeOK() {
-    NS_ASSERTION(!mRuleCascades, "can't toggle quirks style sheet without "
-                                 "clearing rule cascades");
-  }
-#endif
-
 #ifdef XP_WIN
   // Cached theme identifier for the moz-windows-theme media query.
   static uint8_t GetWindowsThemeIdentifier();

layout/style/nsStyleSet.cpp

@@ -260,16 +260,6 @@ nsStyleSet::EndReconstruct()
   GCRuleTrees();
 }
 
-void
-nsStyleSet::SetQuirkStyleSheet(nsIStyleSheet* aQuirkStyleSheet)
-{
-  NS_ASSERTION(aQuirkStyleSheet, "Must have quirk sheet if this is called");
-  NS_ASSERTION(!mQuirkStyleSheet, "Multiple calls to SetQuirkStyleSheet?");
-  NS_ASSERTION(mSheets[eAgentSheet].IndexOf(aQuirkStyleSheet) != -1,
-               "Quirk style sheet not one of our agent sheets?");
-  mQuirkStyleSheet = aQuirkStyleSheet;
-}
-
 typedef nsDataHashtable<nsPtrHashKey<nsINode>, uint32_t> ScopeDepthCache;
 
 // Returns the depth of a style scope element, with 1 being the depth of
@@ -680,35 +670,6 @@ nsStyleSet::EndUpdate()
   return NS_OK;
 }
 
-void
-nsStyleSet::EnableQuirkStyleSheet(bool aEnable)
-{
-  if (!mQuirkStyleSheet) {
-    // SVG-as-an-image doesn't load this sheet
-    return;
-  }
-#ifdef DEBUG
-  bool oldEnabled;
-  {
-    nsCOMPtr<nsIDOMCSSStyleSheet> domSheet =
-      do_QueryInterface(mQuirkStyleSheet);
-    domSheet->GetDisabled(&oldEnabled);
-    oldEnabled = !oldEnabled;
-  }
-#endif
-  mQuirkStyleSheet->SetEnabled(aEnable);
-#ifdef DEBUG
-  // This should always be OK, since SetEnabled should call
-  // ClearRuleCascades.
-  // Note that we can hit this codepath multiple times when document.open()
-  // (potentially implied) happens multiple times.
-  if (mRuleProcessors[eAgentSheet] && aEnable != oldEnabled) {
-    static_cast<nsCSSRuleProcessor*>(static_cast<nsIStyleRuleProcessor*>(
-      mRuleProcessors[eAgentSheet]))->AssertQuirksChangeOK();
-  }
-#endif
-}
-
 template<class T>
 static bool
 EnumRulesMatching(nsIStyleRuleProcessor* aProcessor, void* aData)

layout/style/nsStyleSet.h

@@ -94,9 +94,6 @@ class nsStyleSet
 
   nsRuleNode* GetRuleTree() { return mRuleTree; }
 
-  // enable / disable the Quirk style sheet
-  void EnableQuirkStyleSheet(bool aEnable);
-
   // get a style context for a non-pseudo frame.
   already_AddRefed<nsStyleContext>
   ResolveStyleFor(mozilla::dom::Element* aElement,
@@ -363,11 +360,6 @@ class nsStyleSet
     return mInReconstruct;
   }
 
-  // Let the style set know that a particular sheet is the quirks sheet.  This
-  // sheet must already have been added to the UA sheets.  The pointer must not
-  // be null.  This should only be called once for a given style set.
-  void SetQuirkStyleSheet(nsIStyleSheet* aQuirkStyleSheet);
-
   // Return whether the rule tree has cached data such that we need to
   // do dynamic change handling for changes that change the results of
   // media queries or require rebuilding all style data.
@@ -478,9 +470,6 @@ class nsStyleSet
   // Rule processors for HTML5 scoped style sheets, one per scope.
   nsTArray<nsCOMPtr<nsIStyleRuleProcessor> > mScopedDocSheetRuleProcessors;
 
-  // cached instance for enabling/disabling
-  nsCOMPtr<nsIStyleSheet> mQuirkStyleSheet;
-
   nsRefPtr<nsBindingManager> mBindingManager;
 
   nsRuleNode* mRuleTree; // This is the root of our rule tree.  It is a