SkFixedToDouble uses the decimal floating point string representation
of 1/(2^16) to provide a constant value. This value is exactly
representable by a double but the decimal constant currently used
does not map to this value.
This change modifies this constant to more decimal digits so that
the actual double value desired is created.
Review URL: https://codereview.chromium.org/1097473002
f4fddfc300