Bug 380625. (Not Part Of The Build). Fix cluster count for trimmed spaces.

layout/generic/nsTextFrameThebes.cpp

@@ -5027,6 +5027,18 @@ nsTextFrame::Reflow(nsPresContext*           aPresContext,
     // This is corrected for in nsLineLayout::TrimWhiteSpaceIn.
     PRInt32 numJustifiableCharacters =
       provider.ComputeJustifiableCharacters(offset, charsFit);
+    // Currently canTrimTrailingWhitespace is always true here
+    // because of the !textStyle->WhiteSpaceIsSignificant() test,
+    // but that could change...
+    if (canTrimTrailingWhitespace) {
+      // Count trimmed spaces and add them to the cluster count
+      PRUint32 charIndex = transformedCharsFit;
+      while (charIndex > 0 && mTextRun->GetChar(charIndex - 1) == ' ') {
+        ++textMetrics.mClusterCount;
+        --charIndex;
+      }
+    }
+
     NS_ASSERTION(numJustifiableCharacters <= textMetrics.mClusterCount,
                  "Justifiable characters combined???");
     lineLayout.SetTextJustificationWeights(numJustifiableCharacters,