Fix precision error in https://codereview.chromium.org/1188433011/

include/core/SkMatrix.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 SkMatrix_DEFINED
@@ skipping 705 matching lines @@
                     kRectStaysRect_Mask
     };
 
     SkScalar         fMat[9];
     mutable uint32_t fTypeMask;
 
     /** Are all elements of the matrix finite?
      */
     bool isFinite() const;
 
-    static void ComputeInv(SkScalar dst[9], const SkScalar src[9], SkScalar invDet, bool isPersp);
+    static void ComputeInv(SkScalar dst[9], const SkScalar src[9], double invDet, bool isPersp);
 
     void setScaleTranslate(SkScalar sx, SkScalar sy, SkScalar tx, SkScalar ty) {
         fMat[kMScaleX] = sx;
         fMat[kMSkewX]  = 0;
         fMat[kMTransX] = tx;
 
         fMat[kMSkewY]  = 0;
         fMat[kMScaleY] = sy;
         fMat[kMTransY] = ty;
 
@@ skipping 75 matching lines @@
     static void Persp_pts(const SkMatrix&, SkPoint dst[], const SkPoint[], int);
 
     static void Affine_vpts(const SkMatrix&, SkPoint dst[], const SkPoint[], int);
 
     static const MapPtsProc gMapPtsProcs[];
 
     friend class SkPerspIter;
 };
 
 #endif