Bug 836198: Create a "zombie" state for PresShell and use it for the preloaded TabChild PresShell. r=bz

dom/ipc/TabChild.cpp

@@ -136,6 +136,19 @@ TabChild::PreloadSlowThings()
     tab->TryCacheLoadAndCompileScript(BROWSER_ELEMENT_CHILD_SCRIPT);
     tab->RecvLoadRemoteScript(NS_LITERAL_STRING("chrome://global/content/preload.js"));
 
+    nsCOMPtr<nsIDocShell> docShell = do_GetInterface(tab->mWebNav);
+    nsCOMPtr<nsIPresShell> presShell;
+    if (nsIPresShell* presShell = docShell->GetPresShell()) {
+        // Initialize and do an initial reflow of the about:blank
+        // PresShell to let it preload some things for us.
+        presShell->Initialize(0, 0);
+        nsIDocument* doc = presShell->GetDocument();
+        doc->FlushPendingNotifications(Flush_Layout);
+        // ... but after it's done, make sure it doesn't do any more
+        // work.
+        presShell->MakeZombie();
+    }
+
     sPreallocatedTab = tab;
     ClearOnShutdown(&sPreallocatedTab);
 }

dom/ipc/preload.js

@@ -71,9 +71,6 @@
   Cc["@mozilla.org/uriloader;1"].getService(Ci["nsIURILoader"]);
 
   docShell.isActive = false;
-  docShell.QueryInterface(Ci.nsIWebNavigation)
-          .loadURI("about:blank",
-                   Ci.nsIWebNavigation.LOAD_FLAGS_NONE,
-                   null, null, null);
+  docShell.createAboutBlankContentViewer(null);
 
 })();

layout/base/nsIPresShell.h

@@ -120,10 +120,10 @@ typedef struct CapturingContentInfo {
   nsIContent* mContent;
 } CapturingContentInfo;
 
-// 0841d094-debf-4255-bc7c-c6ff638b2c83
+// da75e297-2c23-43c4-8d7f-96a668e96ba9
 #define NS_IPRESSHELL_IID \
-{ 0x0841d094, 0xdebf, 0x4255, \
-  { 0xbc, 0x7c, 0xc6, 0xff, 0x63, 0x8b, 0x2c, 0x83 } }
+{ 0xda75e297, 0x2c23, 0x43c4, \
+  { 0x8d, 0x7f, 0x96, 0xa6, 0x68, 0xe9, 0x6b, 0xa9 } }
 
 // debug VerifyReflow flags
 #define VERIFY_REFLOW_ON                    0x01
@@ -193,6 +193,18 @@ public:
 
   bool IsDestroying() { return mIsDestroying; }
 
+  /**
+   * Make a one-way transition into a "zombie" state.  In this state,
+   * no reflow is done, no painting is done, and no refresh driver
+   * ticks are processed.  This is a dangerous state: it can leave
+   * areas of the composition target unpainted if callers aren't
+   * careful.  (Don't let your zombie presshell out of the shed.)
+   *
+   * This is used in cases where a presshell is created for reasons
+   * other than reflow/painting.
+   */
+  virtual NS_HIDDEN_(void) MakeZombie() = 0;
+
   /**
    * All frames owned by the shell are allocated from an arena.  They
    * are also recycled using free lists.  Separate free lists are
@@ -1431,6 +1443,7 @@ protected:
   bool                      mStylesHaveChanged : 1;
   bool                      mDidInitialize : 1;
   bool                      mIsDestroying : 1;
+  bool                      mIsZombie : 1;
   bool                      mIsReflowing : 1;
 
   // For all documents we initially lock down painting.

layout/base/nsPresShell.cpp

@@ -1114,6 +1114,13 @@ PresShell::Destroy()
   mHaveShutDown = true;
 }
 
+void
+PresShell::MakeZombie()
+{
+  mIsZombie = true;
+  CancelAllPendingReflows();
+}
+
 void
 nsIPresShell::SetAuthorStyleDisabled(bool aStyleDisabled)
 {
@@ -3762,6 +3769,10 @@ PresShell::FlushPendingNotifications(mozFlushType aType)
 void
 PresShell::FlushPendingNotifications(mozilla::ChangesToFlush aFlush)
 {
+  if (mIsZombie) {
+    return;
+  }
+
   /**
    * VERY IMPORTANT: If you add some sort of new flushing to this
    * method, make sure to add the relevant SetNeedLayoutFlush or
@@ -5293,7 +5304,7 @@ PresShell::Paint(nsView*        aViewToPaint,
   NS_ASSERTION(!mIsDestroying, "painting a destroyed PresShell");
   NS_ASSERTION(aViewToPaint, "null view");
 
-  if (!mIsActive) {
+  if (!mIsActive || mIsZombie) {
     return;
   }
 
@@ -7484,6 +7495,10 @@ PresShell::ScheduleReflowOffTimer()
 bool
 PresShell::DoReflow(nsIFrame* target, bool aInterruptible)
 {
+  if (mIsZombie) {
+    return true;
+  }
+
   target->SchedulePaint();
   nsIFrame *parent = nsLayoutUtils::GetCrossDocParentFrame(target);
   while (parent) {
@@ -9139,10 +9154,12 @@ PresShell::SetIsActive(bool aIsActive)
   if (TabChild* tab = GetTabChildFrom(this)) {
     if (aIsActive) {
       tab->MakeVisible();
-      if (nsIFrame* root = mFrameConstructor->GetRootFrame()) {
-        FrameLayerBuilder::InvalidateAllLayersForFrame(
-          nsLayoutUtils::GetDisplayRootFrame(root));
-        root->SchedulePaint();
+      if (!mIsZombie) {
+        if (nsIFrame* root = mFrameConstructor->GetRootFrame()) {
+          FrameLayerBuilder::InvalidateAllLayersForFrame(
+            nsLayoutUtils::GetDisplayRootFrame(root));
+          root->SchedulePaint();
+        }
       }
     } else {
       tab->MakeHidden();

layout/base/nsPresShell.h

@@ -74,6 +74,7 @@ public:
                                    nsStyleSet* aStyleSet,
                                    nsCompatibility aCompatMode);
   virtual NS_HIDDEN_(void) Destroy();
+  virtual NS_HIDDEN_(void) MakeZombie();
 
   virtual NS_HIDDEN_(nsresult) SetPreferenceStyleRules(bool aForceReflow);