change SkPoint::setLength to set itself to (0,0) if it starting length is degenerate

tests/PointTest.cpp

 
 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 // Unit tests for src/core/SkPoint.cpp and its header
 
 #include "SkPoint.h"
@@ skipping 90 matching lines @@
 
     // now that pt is normalized, we check its length
     length = pt.length();
     REPORTER_ASSERT(reporter, SkScalarNearlyEqual(length, SK_Scalar1));
 }
 
 // test that we handle very small values correctly. i.e. that we can
 // report failure if we try to normalize them.
 static void test_underflow(skiatest::Reporter* reporter) {
     SkPoint pt = { 1.0e-37f, 1.0e-37f };
-    SkPoint copy = pt;
+    const SkPoint empty = { 0, 0 };
 
     REPORTER_ASSERT(reporter, 0 == SkPoint::Normalize(&pt));
-    REPORTER_ASSERT(reporter, pt == copy);  // pt is unchanged
+    REPORTER_ASSERT(reporter, pt == empty);
 
     REPORTER_ASSERT(reporter, !pt.setLength(SK_Scalar1));
-    REPORTER_ASSERT(reporter, pt == copy);  // pt is unchanged
+    REPORTER_ASSERT(reporter, pt == empty);
 }
 
 DEF_TEST(Point, reporter) {
     test_casts(reporter);
 
     static const struct {
         SkScalar fX;
         SkScalar fY;
         SkScalar fLength;
     } gRec[] = {
@@ skipping 21 matching lines @@
         slow.setLength(tests[i]);
         fast.setLengthFast(tests[i]);
 
         if (slow.length() < FLT_MIN && fast.length() < FLT_MIN) continue;
 
         SkScalar ratio = slow.length() / fast.length();
         REPORTER_ASSERT(reporter, ratio > 0.999f);
         REPORTER_ASSERT(reporter, ratio < 1.001f);
     }
 }