SkPDF: fix scalar serialization

gm/skbug_4868.cpp

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm.h"
+
+// clipRect and drawLine should line up exactly when they use the same point.
+// When SkPDF rounds large floats, this doesn't always happen.
+DEF_SIMPLE_GM(skbug_4868, canvas, 32, 32) {
+    canvas->translate(-68.0f, -3378.0f);
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    paint.setStyle(SkPaint::kStroke_Style);
+    canvas->scale(0.56692914f, 0.56692914f);
+    SkRect rc = SkRect::MakeLTRB(158.0f, 5994.80273f, 165.0f, 5998.80225f);
+    canvas->clipRect(rc);
+    canvas->clear(0xFFCECFCE);
+    canvas->drawLine(rc.left(), rc.top(), rc.right(), rc.bottom(), paint);
+    canvas->drawLine(rc.right(), rc.top(), rc.left(), rc.bottom(), paint);
+}