Expose API for gx font variation axes.

include/ports/SkFontMgr.h

Index: include/ports/SkFontMgr.h
diff --git a/include/ports/SkFontMgr.h b/include/ports/SkFontMgr.h
index 96a8501c48561918c8c03213e3198fa78bc61233..3e6c785be9eb66943586b54f15767213d6ad5a52 100644
--- a/include/ports/SkFontMgr.h
+++ b/include/ports/SkFontMgr.h
@@ -8,8 +8,10 @@
 #ifndef SkFontMgr_DEFINED
 #define SkFontMgr_DEFINED
 
-#include "SkRefCnt.h"
 #include "SkFontStyle.h"
+#include "SkRefCnt.h"
+#include "SkScalar.h"
+#include "SkTypes.h"
 
 class SkData;
 class SkFontData;
@@ -100,6 +102,52 @@ public:
      */
     SkTypeface* createFromStream(SkStreamAsset*, int ttcIndex = 0) const;
 
+    struct FontParameters {
+        struct Axis {
+            SkFourByteTag fTag;
+            SkScalar fStyleValue;
+        };
+
+        FontParameters() : fCollectionIndex(0), fAxisCount(0), fAxes(nullptr) {}
+
+        /** Specify the index of the desired font.
+         *
+         *  Font formats like ttc, dfont, cff, cid, pfr, t42, t1, and fon may actually be indexed
+         *  collections of fonts.
+         */
+        FontParameters& setCollectionIndex(int collectionIndex) {
+            fCollectionIndex = collectionIndex;
+            return *this;
+        }
+
+        /** Specify the GX variation axis values.
+         *
+         *  Any axes not specified will use the default value. Specified axes not present in the
+         *  font will be ignored.
+         *
+         *  @param axes not copied. This pointer must remain valid for life of FontParameters.
+         */
+        FontParameters& setAxes(const Axis* axes, int axisCount) {
+            fAxisCount = axisCount;
+            fAxes = axes;
+            return *this;
+        }
+
+        int getCollectionIndex() const {
+            return fCollectionIndex;
+        }
+        const Axis* getAxes(int* axisCount) const {
+            *axisCount = fAxisCount;
+            return fAxes;
+        }
+    private:
+        int fCollectionIndex;
+        int fAxisCount;
+        const Axis* fAxes;
+    };
+    /* Experimental, API subject to change. */
+    SkTypeface* createFromStream(SkStreamAsset*, const FontParameters&) const;
+
     /**
      *  Create a typeface from the specified font data.
      *  Takes ownership of the font data, so the caller should not reference it again.
@@ -144,6 +192,7 @@ protected:
     virtual SkTypeface* onCreateFromData(SkData*, int ttcIndex) const = 0;
     virtual SkTypeface* onCreateFromStream(SkStreamAsset*, int ttcIndex) const = 0;
     // TODO: make pure virtual.
+    virtual SkTypeface* onCreateFromStream(SkStreamAsset*, const FontParameters&) const;
     virtual SkTypeface* onCreateFromFontData(SkFontData*) const;
     virtual SkTypeface* onCreateFromFile(const char path[], int ttcIndex) const = 0;