From ad5fde345ecfb403ac672645777afcb1d2487a84 Mon Sep 17 00:00:00 2001
From: Boris Zbarsky <bzbarsky@mit.edu>
Date: Thu, 2 Feb 2012 11:59:39 -0500
Subject: [PATCH] Bug 723446.  Be a little more careful changing declarations
 on keyframe rules.  r=dbaron

---
 layout/style/nsCSSRules.cpp | 6 +++++-
 xpcom/base/nsAutoPtr.h      | 1 +
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/layout/style/nsCSSRules.cpp b/layout/style/nsCSSRules.cpp
index 49a0c26862d..6dbd76fe84d 100644
--- a/layout/style/nsCSSRules.cpp
+++ b/layout/style/nsCSSRules.cpp
@@ -1964,7 +1964,11 @@ nsCSSKeyframeRule::GetStyle(nsIDOMCSSStyleDeclaration** aStyle)
 void
 nsCSSKeyframeRule::ChangeDeclaration(css::Declaration* aDeclaration)
 {
-  mDeclaration = aDeclaration;
+  // Be careful to not assign to an nsAutoPtr if we would be assigning
+  // the thing it already holds.
+  if (aDeclaration != mDeclaration) {
+    mDeclaration = aDeclaration;
+  }
 
   if (mSheet) {
     mSheet->SetModifiedByChildRule();
diff --git a/xpcom/base/nsAutoPtr.h b/xpcom/base/nsAutoPtr.h
index a32bd263523..02dbbb1f595 100644
--- a/xpcom/base/nsAutoPtr.h
+++ b/xpcom/base/nsAutoPtr.h
@@ -66,6 +66,7 @@ class nsAutoPtr
       void
       assign( T* newPtr )
         {
+          NS_ABORT_IF_FALSE(mRawPtr != newPtr || !newPtr, "This makes no sense!");
           T* oldPtr = mRawPtr;
           mRawPtr = newPtr;
           delete oldPtr;