import from UXP: [gfx] Ensure font entry's unitsPerEm and font extents are initialized when gfxFont is created. (7672f932)

gfx/thebes/gfxFont.cpp

@@ -856,6 +856,10 @@ gfxFont::gfxFont(gfxFontEntry *aFontEntry, const gfxFontStyle *aFontStyle,
     ++gFontCount;
 #endif
     mKerningSet = HasFeatureSet(HB_TAG('k','e','r','n'), mKerningEnabled);
+
+    // Ensure the gfxFontEntry's unitsPerEm and extents fields are initialized,
+    // so that GetFontExtents can use them without risk of races.
+    Unused << mFontEntry->UnitsPerEm();
 }
 
 gfxFont::~gfxFont()