Use pango underline metrics in RenderTextLinux.

ui/gfx/render_text.cc

Index: ui/gfx/render_text.cc
===================================================================
--- ui/gfx/render_text.cc	(revision 140345)
+++ ui/gfx/render_text.cc	(working copy)
@@ -179,9 +179,14 @@
 
 namespace internal {
 
+// Indicates that underline metrics have not been set explicitly.
+const SkScalar kUnderlineMetricsNotSet = -1.0f;

[msw, 2012/06/06 01:12:51]

nit: technically this applies to a single metric value, not both. Maybe use
singular 'metric' terminology: kUnderlineMetricNotSet / "[the|an] underline
metric has".

[Alexei Svitkine (slow), 2012/06/06 14:46:27]

Done.

I've also changed the value to be SK_ScalarNaN, which makes more sense for this
special value.

+
 SkiaTextRenderer::SkiaTextRenderer(Canvas* canvas)
     : canvas_skia_(canvas->sk_canvas()),
-      started_drawing_(false) {
+      started_drawing_(false),
+      underline_thickness_(kUnderlineMetricsNotSet),
+      underline_position_(kUnderlineMetricsNotSet) {
   DCHECK(canvas_skia_);
   paint_.setTextEncoding(SkPaint::kGlyphID_TextEncoding);
   paint_.setStyle(SkPaint::kFill_Style);
@@ -221,7 +226,7 @@
   paint_.setTypeface(typeface);
 }
 
-void SkiaTextRenderer::SetTextSize(int size) {
+void SkiaTextRenderer::SetTextSize(SkScalar size) {
   paint_.setTextSize(size);
 }
 
@@ -252,6 +257,12 @@
   paint_.setShader(shader);
 }
 
+void SkiaTextRenderer::SetUnderlineMetrics(SkScalar thickness,
+                                           SkScalar position) {
+  underline_thickness_ = thickness;
+  underline_position_ = position;
+}
+
 void SkiaTextRenderer::DrawPosText(const SkPoint* pos,
                                    const uint16* glyphs,
                                    size_t glyph_count) {
@@ -304,9 +315,14 @@
   r.fRight = x + width;
 
   if (style.underline) {
-    SkScalar offset = SkScalarMulAdd(text_size, kUnderlineOffset, y);
-    r.fTop = offset;
-    r.fBottom = offset + height;
+    if (underline_position_ == kUnderlineMetricsNotSet) {

[msw, 2012/06/06 01:12:51]

Take the 'not set' path if either value isn't set (also consider checking < 0
instead?).

[Alexei Svitkine (slow), 2012/06/06 14:46:27]

Made the two fields independent - so that none, one, or both could have value
kUnderlineMetricNotSet.

+      SkScalar offset = SkScalarMulAdd(text_size, kUnderlineOffset, y);
+      r.fTop = offset;
+      r.fBottom = offset + height;
+    } else {
+      r.fTop = underline_position_;
+      r.fBottom = r.fTop + underline_thickness_;
+    }
     canvas_skia_->drawRect(r, paint_);
   }
   if (style.strike) {