Reverse the sign of mXOffset in RTL runs so that the offset is always from left to right. Bug 378351, r=roc

gfx/thebes/public/gfxFont.h

@@ -958,7 +958,10 @@ public:
         /** The glyphID if this is a ComplexCluster, or the Unicode character
          * if this is a Missing glyph */
         PRUint32 mGlyphID:31;
-        // The advance, x-offset and y-offset of the glyph, in appunits
+        /** The advance, x-offset and y-offset of the glyph, in appunits
+         *  mAdvance is in the text direction (RTL or LTR)
+         *  mXOffset is always from left to right
+         *  mYOffset is always from bottom to top */   
         PRInt32  mAdvance;
         float    mXOffset, mYOffset;
     };

gfx/thebes/src/gfxWindowsFonts.cpp

@@ -1199,7 +1199,7 @@ public:
                         details->mIsLastGlyph = i == glyphCount - 1;
                         details->mGlyphID = mGlyphs[k + i];
                         details->mAdvance = mAdvances[k + i]*appUnitsPerDevUnit;
-                        details->mXOffset = float(mOffsets[k + i].du)*appUnitsPerDevUnit;
+                        details->mXOffset = float(mOffsets[k + i].du)*appUnitsPerDevUnit*aRun->GetDirection();
                         details->mYOffset = float(mOffsets[k + i].dv)*appUnitsPerDevUnit;
                     }
                     aRun->SetDetailedGlyphs(runOffset, detailedGlyphs.Elements(), glyphCount);