add helper to create fancy underlines

src/core/SkGlyph.h

Index: src/core/SkGlyph.h
diff --git a/src/core/SkGlyph.h b/src/core/SkGlyph.h
index 92f974bc2cf456f8ed367c5f8d0c676baa8a2f26..f9b94a0268f9c9de869f04d09a9cba370c3e42d3 100644
--- a/src/core/SkGlyph.h
+++ b/src/core/SkGlyph.h
@@ -34,12 +34,28 @@ class SkGlyph {
         kSubShiftY = 0
     };
 
- public:
+    // Support horizontal and vertical skipping strike-through / underlines.
+    // The caller walks the linked list looking for a match. For a horizontal underline,
+    // the fBounds contains the top and bottom of the underline. The fInterval pair contains the
+    // beginning and end of of the intersection of the bounds and the glyph's path.
+    // If interval[0] >= interval[1], no intesection was found.
+    struct Intercept {
+        Intercept* fNext;
+        SkScalar   fBounds[2];    // for horz underlines, the boundaries in Y
+        SkScalar   fInterval[2];  // the outside intersections of the axis and the glyph
+    };
+
+    struct PathData {
+        Intercept* fIntercept;
+        SkPath*    fPath;
+    };
+
+public:
     static const SkFixed kSubpixelRound = SK_FixedHalf >> SkGlyph::kSubBits;
     // A value that can never be generated by MakeID.
     static const uint32_t kImpossibleID = ~0;
     void*       fImage;
-    SkPath*     fPath;
+    PathData*   fPathData;
     SkFixed     fAdvanceX, fAdvanceY;
 
     uint16_t    fWidth, fHeight;
@@ -133,7 +149,7 @@ class SkGlyph {
     void initCommon(uint32_t id) {
         fID             = id;
         fImage          = nullptr;
-        fPath           = nullptr;
+        fPathData       = nullptr;
         fMaskFormat     = MASK_FORMAT_UNKNOWN;
         fForceBW        = 0;
     }
@@ -176,7 +192,7 @@ class SkGlyph {
         return ID;
     }
 
-  // FIXME - This is needed because the Android frame work directly
+    // FIXME - This is needed because the Android frame work directly
   // accesses fID. Remove when fID accesses are cleaned up.
 #ifdef SK_BUILD_FOR_ANDROID_FRAMEWORK
   public: