Go back to having UnblockOnload firing onload sync in cases where it's safe.

Attempting to address Tp fallout from bug 294114, r+sr=jst

content/base/public/nsIDocument.h

@@ -93,8 +93,8 @@ class nsILayoutHistoryState;
 
 // IID for the nsIDocument interface
 #define NS_IDOCUMENT_IID      \
-{ 0xd0128d9f, 0x8d36, 0x4944, \
-  { 0xb2, 0x4b, 0x05, 0xba, 0xc2, 0x73, 0x1c, 0x66 } }
+{ 0x6a524f45, 0x4e21, 0x4049, \
+ { 0xb3, 0x57, 0x2d, 0x29, 0x75, 0x76, 0x7a, 0x43 } }
 
 // The base value for the content ID counter.
 // This counter is used by the document to 
@@ -725,12 +725,16 @@ public:
    * should block onload is posted.  onload is guaranteed to not fire until
    * either all calls to BlockOnload() have been matched by calls to
    * UnblockOnload() or the load has been stopped altogether (by the user
-   * pressing the Stop button, say).  onload will fire asynchronously after all
-   * onload blocks have been removed.  It will NOT fire from inside
-   * UnblockOnload.
+   * pressing the Stop button, say).
    */
   virtual void BlockOnload() = 0;
-  virtual void UnblockOnload() = 0;
+  /**
+   * @param aFireSync whether to fire onload synchronously.  If false,
+   * onload will fire asynchronously after all onload blocks have been
+   * removed.  It will NOT fire from inside UnblockOnload.  If true,
+   * onload may fire from inside UnblockOnload.
+   */
+  virtual void UnblockOnload(PRBool aFireSync) = 0;
 
   /**
    * Notification that the page has been shown, for documents which are loaded

content/base/src/nsDocument.cpp

@@ -2281,7 +2281,7 @@ nsDocument::EndLoad()
     observer->EndLoad(this);
   }
   DispatchContentLoadedEvents();
-  UnblockOnload();
+  UnblockOnload(PR_TRUE);
 }
 
 void
@@ -5079,7 +5079,7 @@ nsDocument::BlockOnload()
 }
 
 void
-nsDocument::UnblockOnload()
+nsDocument::UnblockOnload(PRBool aFireSync)
 {
   if (mOnloadBlockCount == 0) {
     NS_NOTREACHED("More UnblockOnload() calls than BlockOnload() calls; dropping call");
@@ -5091,7 +5091,13 @@ nsDocument::UnblockOnload()
   // If mScriptGlobalObject is null, we shouldn't be messing with the loadgroup
   // -- it's not ours.
   if (mOnloadBlockCount == 0 && mScriptGlobalObject) {
-    PostUnblockOnloadEvent();
+    if (aFireSync) {
+      // Increment mOnloadBlockCount, since DoUnblockOnload will decrement it
+      ++mOnloadBlockCount;
+      DoUnblockOnload();
+    } else {
+      PostUnblockOnloadEvent();
+    }
   }
 }
 

content/base/src/nsDocument.h

@@ -646,7 +646,7 @@ public:
   virtual NS_HIDDEN_(already_AddRefed<nsILayoutHistoryState>) GetLayoutHistoryState() const;
 
   virtual NS_HIDDEN_(void) BlockOnload();
-  virtual NS_HIDDEN_(void) UnblockOnload();
+  virtual NS_HIDDEN_(void) UnblockOnload(PRBool aFireSync);
 
   virtual NS_HIDDEN_(void) AddStyleRelevantLink(nsIContent* aContent, nsIURI* aURI);
   virtual NS_HIDDEN_(void) ForgetLink(nsIContent* aContent);

content/base/src/nsImageLoadingContent.cpp

@@ -670,7 +670,7 @@ PR_STATIC_CALLBACK(void)
 DestroyImagePLEvent(PLEvent* aEvent)
 {
   ImageEvent* evt = NS_STATIC_CAST(ImageEvent*, aEvent);
-  evt->mDocument->UnblockOnload();
+  evt->mDocument->UnblockOnload(PR_TRUE);
 
   delete evt;
 }

layout/base/nsPresShell.cpp

@@ -3842,7 +3842,7 @@ struct CantRenderReplacedElementEvent : public PLEvent {
   CantRenderReplacedElementEvent(PresShell* aPresShell,
                                  nsIFrame* aFrame) NS_HIDDEN;
   ~CantRenderReplacedElementEvent() {
-    OurPresShell()->GetDocument()->UnblockOnload();
+    OurPresShell()->GetDocument()->UnblockOnload(PR_TRUE);
   }
   
   NS_HIDDEN_(PresShell*) OurPresShell() {
@@ -6835,7 +6835,7 @@ PresShell::DoneRemovingReflowCommands()
   // can well fire with no presentation in sight.  So just check
   // whether we actually blocked onload.
   if (mRCCreatedDuringLoad == 0 && mDocumentOnloadBlocked) {
-    mDocument->UnblockOnload();
+    mDocument->UnblockOnload(PR_FALSE);
     mDocumentOnloadBlocked = PR_FALSE;
   }
 }