Use pango underline metrics in RenderTextLinux.

ui/gfx/render_text.cc

Index: ui/gfx/render_text.cc
===================================================================
--- ui/gfx/render_text.cc	(revision 141008)
+++ ui/gfx/render_text.cc	(working copy)
@@ -179,9 +179,15 @@
 
 namespace internal {
 
+// Value of |underline_thickness_| that indicates that underline metrics have
+// not been set explicitly.
+const SkScalar kUnderlineMetricsNotSet = -1.0f;
+
 SkiaTextRenderer::SkiaTextRenderer(Canvas* canvas)
     : canvas_skia_(canvas->sk_canvas()),
-      started_drawing_(false) {
+      started_drawing_(false),
+      underline_thickness_(kUnderlineMetricsNotSet),
+      underline_position_(0.0f) {

[msw, 2012/06/12 20:44:39]

You should also init this to kUnderlineMetricsNotSet.
It's better to be explicit with its value.

   DCHECK(canvas_skia_);
   paint_.setTextEncoding(SkPaint::kGlyphID_TextEncoding);
   paint_.setStyle(SkPaint::kFill_Style);
@@ -221,7 +227,7 @@
   paint_.setTypeface(typeface);
 }
 
-void SkiaTextRenderer::SetTextSize(int size) {
+void SkiaTextRenderer::SetTextSize(SkScalar size) {
   paint_.setTextSize(size);
 }
 
@@ -252,6 +258,12 @@
   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 +316,13 @@
   r.fRight = x + width;
 
   if (style.underline) {
-    SkScalar offset = SkScalarMulAdd(text_size, kUnderlineOffset, y);
-    r.fTop = offset;
-    r.fBottom = offset + height;
+    if (underline_thickness_ == kUnderlineMetricsNotSet) {
+      r.fTop = SkScalarMulAdd(text_size, kUnderlineOffset, y);
+      r.fBottom = r.fTop + height;
+    } else {
+      r.fTop = y + underline_position_;

[msw, 2012/06/12 20:44:39]

You should probably DCHECK that underline_position_ is not
kUnderlineMetricsNotSet. I know they're set together now, but that may not
always be the case...

[Alexei Svitkine (slow), 2012/06/12 20:47:43]

-1.0 may be a valid position offset, but definitely never a valid thickness.

[msw, 2012/06/12 21:28:12]

Fair enough, then it might be worthwhile to add a comment at the declaration /
setter that the two must be set together, etc.

+      r.fBottom = r.fTop + underline_thickness_;
+    }
     canvas_skia_->drawRect(r, paint_);
   }
   if (style.strike) {