Bug 407015. Dropdown listboxes should not propagate computed height from the scrollframe to its scrolled content. r+sr=dbaron

layout/forms/nsListControlFrame.cpp

@@ -787,6 +787,12 @@ nsListControlFrame::GetScrollbarStyles() const
                                                 verticalStyle);
 }
 
+PRBool
+nsListControlFrame::ShouldPropagateComputedHeightToScrolledContent() const
+{
+  return !IsInDropDownMode();
+}
+
 //---------------------------------------------------------
 PRBool 
 nsListControlFrame::IsOptionElement(nsIContent* aContent)

layout/forms/nsListControlFrame.h

@@ -144,6 +144,7 @@ public:
   virtual void SetFocus(PRBool aOn = PR_TRUE, PRBool aRepaint = PR_FALSE);
 
   virtual nsGfxScrollFrameInner::ScrollbarStyles GetScrollbarStyles() const;
+  virtual PRBool ShouldPropagateComputedHeightToScrolledContent() const;
 
     // for accessibility purposes
 #ifdef ACCESSIBILITY

layout/generic/nsGfxScrollFrame.cpp

@@ -437,6 +437,11 @@ nsHTMLScrollFrame::ReflowScrolledFrame(ScrollReflowState* aState,
   nscoord computedHeight = aState->mReflowState.ComputedHeight();
   nscoord computedMinHeight = aState->mReflowState.mComputedMinHeight;
   nscoord computedMaxHeight = aState->mReflowState.mComputedMaxHeight;
+  if (!ShouldPropagateComputedHeightToScrolledContent()) {
+    computedHeight = NS_UNCONSTRAINEDSIZE;
+    computedMinHeight = 0;
+    computedMaxHeight = NS_UNCONSTRAINEDSIZE;
+  }
   if (aAssumeHScroll) {
     nsSize hScrollbarPrefSize = 
       mInner.mHScrollbarBox->GetPrefSize(const_cast<nsBoxLayoutState&>(aState->mBoxState));
@@ -446,7 +451,7 @@ nsHTMLScrollFrame::ReflowScrolledFrame(ScrollReflowState* aState,
     if (computedMaxHeight != NS_UNCONSTRAINEDSIZE)
       computedMaxHeight = PR_MAX(0, computedMaxHeight - hScrollbarPrefSize.height);
   }
-  
+
   if (aAssumeVScroll) {
     nsSize vScrollbarPrefSize = 
       mInner.mVScrollbarBox->GetPrefSize(const_cast<nsBoxLayoutState&>(aState->mBoxState));

layout/generic/nsGfxScrollFrame.h

@@ -401,6 +401,13 @@ protected:
   // NS_FRAME_FIRST_REFLOW set are NOT "initial" as far as we're concerned.
   PRBool InInitialReflow() const;
   
+  /**
+   * Override this to return false if computed height/min-height/max-height
+   * should NOT be propagated to child content.
+   * nsListControlFrame uses this.
+   */
+  virtual PRBool ShouldPropagateComputedHeightToScrolledContent() const { return PR_TRUE; }
+
 private:
   friend class nsGfxScrollFrameInner;
   nsGfxScrollFrameInner mInner;