Bug 372237. Never set TRUNCATED reflow status if the available height is unconstrained, even if the height happens to exceed the constant we use to indicate unconstrained height. r+sr=dbaron

layout/generic/nsHTMLReflowState.cpp

@@ -2106,3 +2106,16 @@ nsHTMLReflowState::ComputeMinMaxValues(nscoord aContainingBlockWidth,
     mComputedMaxHeight = mComputedMinHeight;
   }
 }
+
+void
+nsHTMLReflowState::SetTruncated(const nsHTMLReflowMetrics& aMetrics,
+                                nsReflowStatus* aStatus) const
+{
+  if (availableHeight != NS_UNCONSTRAINEDSIZE &&
+      availableHeight < aMetrics.height &&
+      !mFlags.mIsTopOfPage) {
+    *aStatus |= NS_FRAME_TRUNCATED;
+  } else {
+    *aStatus &= ~NS_FRAME_TRUNCATED;
+  }
+}

layout/generic/nsHTMLReflowState.h

@@ -419,6 +419,8 @@ public:
   nscoord ComputedWidth() const { return mComputedWidth; }
   void SetComputedWidth(nscoord aComputedWidth);
 
+  void SetTruncated(const nsHTMLReflowMetrics& aMetrics, nsReflowStatus* aStatus) const;
+
 protected:
 
   void InitCBReflowState();

layout/generic/nsIFrame.h

@@ -367,11 +367,7 @@ typedef PRUint32 nsReflowStatus;
 #define NS_FRAME_IS_TRUNCATED(status) \
   (0 != ((status) & NS_FRAME_TRUNCATED))
 #define NS_FRAME_SET_TRUNCATION(status, aReflowState, aMetrics) \
-  if (!aReflowState.mFlags.mIsTopOfPage &&                      \
-      aReflowState.availableHeight < aMetrics.height)           \
-    status |= NS_FRAME_TRUNCATED;                               \
-  else                                                          \
-    status &= ~NS_FRAME_TRUNCATED;
+  aReflowState.SetTruncated(aMetrics, &status);
 
 //----------------------------------------------------------------------