Adding code to calculate Underline Thickness from Font Metrics, this will be useful when Skia is us…

src/core/SkPaint.cpp

Index: src/core/SkPaint.cpp
diff --git a/src/core/SkPaint.cpp b/src/core/SkPaint.cpp
index c3f217cefc60e5501e08a88755b5f537dbcb956c..9e4a26448f28d80dfe9a4eab3d7853774ea32487 100644
--- a/src/core/SkPaint.cpp
+++ b/src/core/SkPaint.cpp
@@ -1296,6 +1296,8 @@ SkScalar SkPaint::getFontMetrics(FontMetrics* metrics, SkScalar zoom) const {
         metrics->fXMin = SkScalarMul(metrics->fXMin, scale);
         metrics->fXMax = SkScalarMul(metrics->fXMax, scale);
         metrics->fXHeight = SkScalarMul(metrics->fXHeight, scale);
+        metrics->fUnderlineThickness = SkScalarMul(metrics->fUnderlineThickness, scale);
+        metrics->fUnderlinePosition = SkScalarMul(metrics->fUnderlinePosition, scale);
     }
     return metrics->fDescent - metrics->fAscent + metrics->fLeading;
 }
@@ -2257,6 +2259,26 @@ const SkRect& SkPaint::doComputeFastBounds(const SkRect& origSrc,
     return *storage;
 }
 
+bool SkPaint::FontMetrics::hasUnderlineThickness(SkScalar* thickness) const {
+    if (SkToBool(fFlags & kUnderlineThinknessIsValid_Flag))
+    {
+        *thickness = fUnderlineThickness;
+        return true;
+    }
+    *thickness = 0;
+    return false;
+}
+
+bool SkPaint::FontMetrics::hasUnderlinePosition(SkScalar* thickness) const {
+    if (SkToBool(fFlags & kUnderlinePositionIsValid_Flag))
+    {
+        *thickness = fUnderlinePosition;
+        return true;
+    }
+    *thickness = 0;
+    return false;
+}
+
 #ifdef SK_DEVELOPER
 void SkPaint::toString(SkString* str) const {
     str->append("<dl><dt>SkPaint:</dt><dd><dl>");