Save and expose on nsFontInflationData the width of the nearest common ancestor of the inflated descendants. (Bug 747720, patch 1) r=roc

This width will be used in patch 3.

layout/generic/nsFontInflationData.cpp

@@ -235,6 +235,7 @@ nsFontInflationData::UpdateWidth(const nsHTMLReflowState &aReflowState)
     mTextDirty = true;
   }
 
+  mNCAWidth = newNCAWidth;
   mTextThreshold = newTextThreshold;
   mInflationEnabled = mTextAmount >= mTextThreshold;
 }

layout/generic/nsFontInflationData.h

@@ -64,6 +64,10 @@ public:
     return mInflationEnabled;
   }
 
+  nscoord EffectiveWidth() const {
+    return mNCAWidth;
+  }
+
 private:
 
   nsFontInflationData(nsIFrame* aBFCFrame);
@@ -94,6 +98,7 @@ private:
   }
 
   nsIFrame *mBFCFrame;
+  nscoord mNCAWidth;
   nscoord mTextAmount, mTextThreshold;
   bool mInflationEnabled; // for this BFC
   bool mTextDirty;