add rounding-using-doubles methods on SkScalar and SkRect

tests/ScalarTest.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.
  */
 
 #include "SkFloatingPoint.h"
 #include "SkMath.h"
 #include "SkPoint.h"
 #include "SkRandom.h"
 #include "SkRect.h"
 #include "Test.h"
 
+static void test_roundtoint(skiatest::Reporter* reporter) {
+    SkScalar x = 0.49999997;
+    int ix = SkScalarRoundToInt(x);
+    // We "should" get 0, since x < 0.5, but we don't due to float addition rounding up the low
+    // bit after adding 0.5.
+    REPORTER_ASSERT(reporter, 1 == ix);
+
+    // This version explicitly performs the +0.5 step using double, which should avoid losing the
+    // low bits.
+    ix = SkDScalarRoundToInt(x);
+    REPORTER_ASSERT(reporter, 0 == ix);
+}
+
 struct PointSet {
     const SkPoint* fPts;
     size_t         fCount;
     bool           fIsFinite;
 };
 
 static void test_isRectFinite(skiatest::Reporter* reporter) {
     static const SkPoint gF0[] = {
         { 0, 0 }, { 1, 1 }
     };
@@ skipping 155 matching lines @@
 
     test_isRectFinite(reporter);
 }
 
 #if defined _WIN32
 #pragma warning ( pop )
 #endif
 
 DEF_TEST(Scalar, reporter) {
     test_isfinite(reporter);
+    test_roundtoint(reporter);
 }