use strikethrough position for middle`

Author: asturur

src/CanvasRenderingContext2d.cc

@@ -2403,11 +2403,16 @@ NAN_METHOD(Context2d::StrokeText) {
 inline double getBaselineAdjustment(PangoLayout* layout, short baseline) {
   PangoRectangle logical_rect;
   PangoLayout* measureLayout = pango_layout_copy(layout);
+  PangoFontMetrics *metrics;
   pango_layout_set_text(measureLayout, "gjĮ測試ÅÊ", -1);
   pango_layout_line_get_extents(pango_layout_get_line(measureLayout, 0), NULL, &logical_rect);
+  metrics = PANGO_LAYOUT_GET_METRICS(measureLayout);
+  int strike_thickness = pango_font_metrics_get_strikethrough_thickness(metrics);
+  int strike_position = pango_font_metrics_get_strikethrough_position(metrics);
   double scale = 1.0 / PANGO_SCALE;
   double ascent = scale * pango_layout_get_baseline(measureLayout);
   double descent = scale * logical_rect.height - ascent;
+  double middle = ascent - (scale * strike_position) + (scale * strike_thickness / 2);
   // 0.072 is a constant that has been chosen comparing the canvas output
   // if some code change, this constant can be changed too to keep results aligned
   double correction_factor = scale * logical_rect.height * 0.072;