move SkScalarMean into its only caller, reducing out public API exposure

BUG=

Review URL: https://codereview.chromium.org/117973002

git-svn-id: http://skia.googlecode.com/svn/trunk@12732 2bbb7eff-a529-9590-31e7-b0007b416f81

include/core/SkScalar.h

@@ -139,9 +139,6 @@ inline SkScalar SkScalarSquare(SkScalar x) { return x * x; }
 /** Returns the average of two SkScalars (a+b)/2
 */
 #define SkScalarAve(a, b)       (((a) + (b)) * 0.5f)
-/** Returns the geometric mean of two SkScalars
-*/
-#define SkScalarMean(a, b)      sk_float_sqrt((float)(a) * (b))
 /** Returns one half of the specified SkScalar
 */
 #define SkScalarHalf(a)         ((a) * 0.5f)

src/core/SkMatrix.cpp

@@ -1177,7 +1177,8 @@ SkScalar SkMatrix::mapRadius(SkScalar radius) const {
     SkScalar d0 = vec[0].length();
     SkScalar d1 = vec[1].length();
 
-    return SkScalarMean(d0, d1);
+    // return geometric mean
+    return SkScalarSqrt(d0 * d1);
 }
 
 ///////////////////////////////////////////////////////////////////////////////