add rounding-using-doubles methods on SkScalar and SkRect

src/core/SkScan_Path.cpp

 /*
  * 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.
  */
 
 #include "SkScanPriv.h"
 #include "SkBlitter.h"
 #include "SkEdge.h"
@@ skipping 584 matching lines @@
     SkRegion finiteClip;
     if (clip_to_limit(origClip, &finiteClip)) {
         if (finiteClip.isEmpty()) {
             return;
         }
         clipPtr = &finiteClip;
     }
         // don't reference "origClip" any more, just use clipPtr
 
     SkIRect ir;
-    path.getBounds().round(&ir);
+    // We deliberately call dround() instead of round(), since we can't afford to generate a
+    // bounds that is tighter than the corresponding SkEdges. The edge code basically converts
+    // the floats to fixed, and then "rounds". If we called round() instead of dround() here,
+    // we could generate the wrong ir for values like 0.4999997.
+    path.getBounds().dround(&ir);
     if (ir.isEmpty()) {
         if (path.isInverseFillType()) {
             blitter->blitRegion(*clipPtr);
         }
         return;
     }
 
     SkScanClipper clipper(blitter, clipPtr, ir, path.isInverseFillType());
 
     blitter = clipper.getBlitter();
@@ skipping 104 matching lines @@
         clipRgn = &wrap.getRgn();
         blitter = wrap.getBlitter();
     }
 
     SkScanClipper clipper(blitter, clipRgn, ir);
     blitter = clipper.getBlitter();
     if (NULL != blitter) {
         sk_fill_triangle(pts, clipper.getClipRect(), blitter, ir);
     }
 }