Optimize ParamTraits<float> and ParamTraits<double>

Optimize ParamTraits<float> and ParamTraits<double>

These function become hot on some benchmarks. WriteData is inefficient because
it writes the length, even though it's known on the reader side (compile-time
constant).
For <float> we can simply use WriteFloat. For <double> we can use WriteBytes
instead of WriteData.

BUG=307480
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=232060

[jam, 2013-10-24 16:17:23]

lgtm

if you change the serialization format, you need to update the reference_builds
http://src.chromium.org/viewvc/chrome/trunk/deps/reference_builds/

[commit-bot: I haz the power, 2013-10-31 04:57:04]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/piman@chromium.org/39363002/90001

[commit-bot: I haz the power, 2013-10-31 09:27:32]

Change committed as 232060