SkPDF: re-work SkPDFUtils::FloatToDecimal

tests/PDFPrimitivesTest.cpp

Index: tests/PDFPrimitivesTest.cpp
diff --git a/tests/PDFPrimitivesTest.cpp b/tests/PDFPrimitivesTest.cpp
index 9e2a89e60953b067faf69e588a05bad9b6a07657..2557ca06a30687b7f6c1953e2721e18b65f13904 100644
--- a/tests/PDFPrimitivesTest.cpp
+++ b/tests/PDFPrimitivesTest.cpp
@@ -210,7 +210,7 @@ static void TestPDFUnion(skiatest::Reporter* reporter) {
     ASSERT_EMIT_EQ(reporter, biggerScalar, "50000000");
 
     SkPDFUnion smallestScalar = SkPDFUnion::Scalar(1.0f / 65536);
-    ASSERT_EMIT_EQ(reporter, smallestScalar, ".0000152587890");
+    ASSERT_EMIT_EQ(reporter, smallestScalar, ".0000152587891");

[tomhudson, 2016/07/15 20:45:42]

One digit change? How did this ever work? Or is there something subtle here that
isn't obvious from reading the code?

[hal.canary, 2016/07/17 02:33:42]

Both values round back to the original float value, which is somewhere in
between them:
    Before: .0000152587890
    After:  .0000152587891
    Exact:  .0000152587890625

    assert(1.0f / 65536 == (float)atof(".0000152587890"));
    assert(1.0f / 65536 == (float)atof(".0000152587891"));

 
     SkPDFUnion stringSimple = SkPDFUnion::String("test ) string ( foo");
     ASSERT_EMIT_EQ(reporter, stringSimple, "(test \\) string \\( foo)");