Bug 1238337. If the intrinsic size of the image hasn't changed then we don't need to do a new predictive image decode. r=mats

nsImageFrame::OnSizeAvailable will update the intrinsic ratio and ask for a reflow. Then nsImageFrame::NotifyNewCurrentRequest will be called when the image is finished loading. It previously would do a predictive decode if the intrinsic size hadn't changed.

This was a mistake in http://hg.mozilla.org/mozilla-central/rev/146f1bea4147 (bug 1151359).

OnSizeAvailable has this structure:

  if (intrinsicSizeChanged && gotInitialReflow) {
    if (!sizeConstrained) {
      requestReflow();
    }
  }

NotifyNewCurrentRequest has this structure:

  if (gotInitialReflow) {
    if (!sizeConstrained && intrinsicSizeChanged) {
      requestReflow();
    }
  }

Bug 1151359 added a predictive decode in a new else branch to both inner if statements. The meaning of this is obviously quite different.

layout/generic/nsImageFrame.cpp

@@ -681,16 +681,18 @@ nsImageFrame::NotifyNewCurrentRequest(imgIRequest *aRequest,
   }
 
   if (mState & IMAGE_GOTINITIALREFLOW) { // do nothing if we haven't gotten the initial reflow yet
-    if (!(mState & IMAGE_SIZECONSTRAINED) && intrinsicSizeChanged) {
-      nsIPresShell *presShell = PresContext()->GetPresShell();
-      if (presShell) { 
-        presShell->FrameNeedsReflow(this, nsIPresShell::eStyleChange,
-                                    NS_FRAME_IS_DIRTY);
+    if (intrinsicSizeChanged) {
+      if (!(mState & IMAGE_SIZECONSTRAINED)) {
+        nsIPresShell *presShell = PresContext()->GetPresShell();
+        if (presShell) {
+          presShell->FrameNeedsReflow(this, nsIPresShell::eStyleChange,
+                                      NS_FRAME_IS_DIRTY);
+        }
+      } else {
+        // We've already gotten the initial reflow, and our size hasn't changed,
+        // so we're ready to request a decode.
+        MaybeDecodeForPredictedSize();
       }
-    } else {
-      // We've already gotten the initial reflow, and our size hasn't changed,
-      // so we're ready to request a decode.
-      MaybeDecodeForPredictedSize();
     }
     // Update border+content to account for image change
     InvalidateFrame();