Factor code to rotate a canvas about a point.

gm/typeface.cpp

Index: gm/typeface.cpp
diff --git a/gm/typeface.cpp b/gm/typeface.cpp
index 34420dbee1868d177ec256977528cafb72546933..c611dca211401ed8d48663455f11c31530ff2914 100644
--- a/gm/typeface.cpp
+++ b/gm/typeface.cpp
@@ -12,6 +12,7 @@
 #include "SkSurfaceProps.h"
 #include "SkTypeface.h"
 #include "SkTypes.h"
+#include "sk_tool_utils.h"
 
 static void getGlyphPositions(const SkPaint& paint, const uint16_t glyphs[],
                              int count, SkScalar x, SkScalar y, SkPoint pos[]) {
@@ -154,20 +155,9 @@ private:
     typedef skiagm::GM INHERITED;
 };
 
-static void rotate_about(SkCanvas* canvas,
-                         SkScalar degrees,
-                         SkScalar px, SkScalar py) {
-    canvas->translate(px, py);
-    canvas->rotate(degrees);
-    canvas->translate(-px, -py);
-}
-
 class TypefaceRenderingGM : public skiagm::GM {
     sk_sp<SkTypeface> fFace;
 
-public:
-    TypefaceRenderingGM() { }
-
 protected:
     void onOnceBeforeDraw() override {
         fFace = MakeResourceAsTypeface("/fonts/hintgasp.ttf");
@@ -256,8 +246,8 @@ protected:
                         for (const bool& rotateABit : rotateABitTypes) {
                             SkAutoCanvasRestore acr(canvas, true);
                             if (rotateABit) {
-                                rotate_about(canvas, 2, x + subpixel.offset.x(),
-                                                        y + subpixel.offset.y());
+                                sk_tool_utils::rotate_about(canvas, 2, x + subpixel.offset.x(),
+                                                                       y + subpixel.offset.y());
                             }
                             canvas->drawText("A", 1, x + subpixel.offset.x(),
                                                      y + subpixel.offset.y(), paint);