The slow codepaths for fixed background-attachment should only apply when there's a background image. b=258793 r+sr=roc

content/shared/public/nsStyleStruct.h

@@ -187,6 +187,14 @@ struct nsStyleBackground : public nsStyleStruct {
             (NS_STYLE_BG_COLOR_TRANSPARENT | NS_STYLE_BG_IMAGE_NONE)) ==
             (NS_STYLE_BG_COLOR_TRANSPARENT | NS_STYLE_BG_IMAGE_NONE);
   }
+
+  PRBool HasFixedBackground() const
+  {
+    // We have to take slower codepaths for fixed background attachment,
+    // but we don't want to do that when there's no image.
+    return mBackgroundAttachment == NS_STYLE_BG_ATTACHMENT_FIXED &&
+           mBackgroundImage;
+  }
 };
 
 #define BORDER_COLOR_DEFINED      0x80  

layout/generic/nsContainerFrame.cpp

@@ -572,8 +572,7 @@ SyncFrameViewGeometryDependentProperties(nsPresContext*  aPresContext,
 
   // background-attachment: fixed is not really geometry dependent, but
   // we set it here because it's cheap to do so
-  PRBool fixedBackground = hasBG &&
-    NS_STYLE_BG_ATTACHMENT_FIXED == bg->mBackgroundAttachment;
+  PRBool fixedBackground = hasBG && bg->HasFixedBackground();
   // If the frame has a fixed background attachment, then indicate that the
   // view's contents should be repainted and not bitblt'd
   vm->SetViewBitBltEnabled(aView, !fixedBackground);
@@ -901,8 +900,7 @@ nsContainerFrame::FrameNeedsView(nsIFrame* aFrame)
   PRBool hasBackground = 
     nsCSSRendering::FindBackground(aFrame->GetPresContext(),
                                    aFrame, &color, &isCanvas);
-  if (hasBackground &&
-      NS_STYLE_BG_ATTACHMENT_FIXED == color->mBackgroundAttachment) {
+  if (hasBackground && color->HasFixedBackground()) {
     return PR_TRUE;
   }
     

layout/html/base/src/nsContainerFrame.cpp

@@ -572,8 +572,7 @@ SyncFrameViewGeometryDependentProperties(nsPresContext*  aPresContext,
 
   // background-attachment: fixed is not really geometry dependent, but
   // we set it here because it's cheap to do so
-  PRBool fixedBackground = hasBG &&
-    NS_STYLE_BG_ATTACHMENT_FIXED == bg->mBackgroundAttachment;
+  PRBool fixedBackground = hasBG && bg->HasFixedBackground();
   // If the frame has a fixed background attachment, then indicate that the
   // view's contents should be repainted and not bitblt'd
   vm->SetViewBitBltEnabled(aView, !fixedBackground);
@@ -901,8 +900,7 @@ nsContainerFrame::FrameNeedsView(nsIFrame* aFrame)
   PRBool hasBackground = 
     nsCSSRendering::FindBackground(aFrame->GetPresContext(),
                                    aFrame, &color, &isCanvas);
-  if (hasBackground &&
-      NS_STYLE_BG_ATTACHMENT_FIXED == color->mBackgroundAttachment) {
+  if (hasBackground && color->HasFixedBackground()) {
     return PR_TRUE;
   }
     

layout/style/nsStyleStruct.h

@@ -187,6 +187,14 @@ struct nsStyleBackground : public nsStyleStruct {
             (NS_STYLE_BG_COLOR_TRANSPARENT | NS_STYLE_BG_IMAGE_NONE)) ==
             (NS_STYLE_BG_COLOR_TRANSPARENT | NS_STYLE_BG_IMAGE_NONE);
   }
+
+  PRBool HasFixedBackground() const
+  {
+    // We have to take slower codepaths for fixed background attachment,
+    // but we don't want to do that when there's no image.
+    return mBackgroundAttachment == NS_STYLE_BG_ATTACHMENT_FIXED &&
+           mBackgroundImage;
+  }
 };
 
 #define BORDER_COLOR_DEFINED      0x80  

layout/xul/base/src/nsBoxFrame.cpp

@@ -2490,7 +2490,7 @@ nsBoxFrame::CreateViewForFrame(nsPresContext*  aPresContext,
     }
 
     // See if the frame has a fixed background attachment
-    if (hasBG && NS_STYLE_BG_ATTACHMENT_FIXED == bg->mBackgroundAttachment) {
+    if (hasBG && bg->HasFixedBackground()) {
       aForce = PR_TRUE;
       fixedBackgroundAttachment = PR_TRUE;
     }