Make bigger string size in RenderTextHarfBuzz.

ui/gfx/render_text_harfbuzz.cc

Index: ui/gfx/render_text_harfbuzz.cc
diff --git a/ui/gfx/render_text_harfbuzz.cc b/ui/gfx/render_text_harfbuzz.cc
index 0580abe3375e09bddae437c08a958ee6a7d16977..0861999052d68520595e9f283e885483aac47622 100644
--- a/ui/gfx/render_text_harfbuzz.cc
+++ b/ui/gfx/render_text_harfbuzz.cc
@@ -233,6 +233,8 @@ class HarfBuzzLineBreaker {
         run_list_(run_list),
         text_x_(0),
         line_x_(0),
+        max_top_(0),
+        max_bottom_(0),
         max_descent_(0),
         max_ascent_(0) {
     DCHECK_EQ(multiline_, (words_ != nullptr));
@@ -256,10 +258,15 @@ class HarfBuzzLineBreaker {
   // Finishes line breaking and outputs the results. Can be called at most once.
   void Finalize(std::vector<internal::Line>* lines, SizeF* size) {
     DCHECK(!lines_.empty());
+    float trailing_height = std::max(0.f, max_bottom_ - max_descent_);
     // Add an empty line to finish the line size calculation and remove it.
     AdvanceLine();
     lines_.pop_back();
     *size = total_size_;
+    // Add extra space below the last line, because some characters (eg.
+    // underscore) may be drawn under the descent. See http://crbug.com/459812
+    // and the comments in AdvanceLine() below.

[msw, 2015/02/26 00:47:21]

nit: you can remove this line "// and the comments in AdvanceLine() below."

+    size->Enlarge(0, trailing_height);
     lines->swap(lines_);
   }
 
@@ -384,10 +391,23 @@ class HarfBuzzLineBreaker {
       line->size.set_height(std::max(min_height_, max_descent_ + max_ascent_));
       line->baseline =
           std::max(min_baseline_, SkScalarRoundToInt(max_ascent_));
-      line->preceding_heights = std::ceil(total_size_.height());
-      total_size_.set_height(total_size_.height() + line->size.height());
+      // Line height is assumed to be the height between the ascent and the

[msw, 2015/02/26 00:47:21]

nit: consider just using a comment like that above: "Add extra space above the
first line, because some characters (eg. A-ring) may be drawn above the ascent.
See http://crbug.com/459812"

+      // descent, however some diacritic marks may appear above the ascent.
+      // Therefore prepare enough space above the first line. Note that the
+      // line height wouldn't be the height between top and bottom to avoid
+      // making extra space between lines. See http://crbug.com/459812
+      if (line == &lines_.front()) {
+        line->preceding_heights =
+            std::ceil(std::max(0.f, max_top_ - max_ascent_));
+        total_size_.set_height(line->preceding_heights + line->size.height());
+      } else {
+        line->preceding_heights = std::ceil(total_size_.height());
+        total_size_.set_height(total_size_.height() + line->size.height());
+      }
       total_size_.set_width(std::max(total_size_.width(), line->size.width()));
     }
+    max_top_ = 0;
+    max_bottom_ = 0;
     max_descent_ = 0;
     max_ascent_ = 0;
     line_x_ = 0;
@@ -422,8 +442,10 @@ class HarfBuzzLineBreaker {
 
     line->size.set_width(line->size.width() + width);
     max_descent_ = std::max(max_descent_, metrics.fDescent);
-    // fAscent is always negative.
+    max_bottom_ = std::max(max_bottom_, metrics.fBottom);
+    // fAscent and fTop are always negative.
     max_ascent_ = std::max(max_ascent_, -metrics.fAscent);
+    max_top_ = std::max(max_top_, -metrics.fTop);
 
     if (run.is_rtl) {
       rtl_segments_.push_back(
@@ -452,6 +474,8 @@ class HarfBuzzLineBreaker {
   SkScalar text_x_;
   SkScalar line_x_;
 
+  float max_top_;
+  float max_bottom_;
   float max_descent_;
   float max_ascent_;