Bug 398181: Use NSCoordSaturatingAdd/Subtract in 3 places where we might have unconstrained heights. r+sr+a=roc

layout/generic/nsFrame.cpp

@@ -2866,12 +2866,12 @@ nsIFrame::InlinePrefWidthData::ForceBreak(nsIRenderingContext *aRenderingContext
     if (floats_cur > floats_done)
       floats_done = floats_cur;
 
-    currentLine += floats_done;
+    currentLine = NSCoordSaturatingAdd(currentLine, floats_done);
 
     floats.Clear();
   }
 
-  currentLine -= trailingWhitespace;
+  currentLine = NSCoordSaturatingSubtract(currentLine, trailingWhitespace, nscoord_MAX);
   prevLines = PR_MAX(prevLines, currentLine);
   currentLine = trailingWhitespace = 0;
 }

layout/generic/nsTextFrameThebes.cpp

@@ -4933,7 +4933,7 @@ nsTextFrame::AddInlinePrefWidthForFlow(nsIRenderingContext *aRenderingContext,
     // onto one line, so just measure it
     nscoord width =
       NSToCoordCeil(mTextRun->GetAdvanceWidth(start, flowEndInTextRun - start, &provider));
-    aData->currentLine += width;
+    aData->currentLine = NSCoordSaturatingAdd(aData->currentLine, width);
 
     PRUint32 trimStart = GetEndOfTrimmedText(provider.GetFragment(), start,
                                              flowEndInTextRun, &iter);