SkPDF: fix scalar serialization

src/pdf/SkPDFUtils.h

Index: src/pdf/SkPDFUtils.h
diff --git a/src/pdf/SkPDFUtils.h b/src/pdf/SkPDFUtils.h
index 0aa05a088a8e59898a9d4d1e776d9ede37fd322f..814d77193cb38d5bd803f847cf36a5e6ab2d1603 100644
--- a/src/pdf/SkPDFUtils.h
+++ b/src/pdf/SkPDFUtils.h
@@ -58,6 +58,14 @@ public:
     static void DrawFormXObject(int objectIndex, SkWStream* content);
     static void ApplyGraphicState(int objectIndex, SkWStream* content);
     static void ApplyPattern(int objectIndex, SkWStream* content);
+
+    // 3 = '-', '.', and '\0' characters.
+    // 9 = number of significant digits
+    // abs(FLT_MIN_10_EXP) = number of zeros in FLT_MIN
+    static const size_t kMaximumFloatDecimalLength = 3 + 9 - FLT_MIN_10_EXP;
+    // FloatToDecimal is exposed for unit tests.
+    static size_t FloatToDecimal(float value,
+                                 char output[kMaximumFloatDecimalLength]);
     static void AppendScalar(SkScalar value, SkWStream* stream);
     static SkString FormatString(const char* input, size_t len);
 };