Factor code to rotate a canvas about a point.

include/core/SkCanvas.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkCanvas_DEFINED
 #define SkCanvas_DEFINED
 
@@ skipping 401 matching lines @@
         @param dy   The distance to translate in Y
     */
     void translate(SkScalar dx, SkScalar dy);
 
     /** Preconcat the current matrix with the specified scale.
         @param sx   The amount to scale in X
         @param sy   The amount to scale in Y
     */
     void scale(SkScalar sx, SkScalar sy);
 
-    /** Preconcat the current matrix with the specified rotation.
+    /** Preconcat the current matrix with the specified rotation about the origin.
         @param degrees  The amount to rotate, in degrees
     */
     void rotate(SkScalar degrees);
 
+    /** Preconcat the current matrix with the specified rotation about a given point.
+        @param degrees  The amount to rotate, in degrees
+        @param px  The x coordinate of the point to rotate about.
+        @param py  The y coordinate of the point to rotate about.
+    */
+    void rotate(SkScalar degrees, SkScalar px, SkScalar py);
+
     /** Preconcat the current matrix with the specified skew.
         @param sx   The amount to skew in X
         @param sy   The amount to skew in Y
     */
     void skew(SkScalar sx, SkScalar sy);
 
     /** Preconcat the current matrix with the specified matrix.
         @param matrix   The matrix to preconcatenate with the current matrix
     */
     void concat(const SkMatrix& matrix);
@@ skipping 1161 matching lines @@
 
 class SkCanvasClipVisitor {
 public:
     virtual ~SkCanvasClipVisitor();
     virtual void clipRect(const SkRect&, SkRegion::Op, bool antialias) = 0;
     virtual void clipRRect(const SkRRect&, SkRegion::Op, bool antialias) = 0;
     virtual void clipPath(const SkPath&, SkRegion::Op, bool antialias) = 0;
 };
 
 #endif