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

Review URL: https://codereview.chromium.org/39363002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232060 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232060
Webrequest: Say in docs that not all events are supported for all schemes

As the linked bug mentions, e.g., ftp: requests do not observe onSendHeaders and others, file: is another example with a reduced set of events.

NOTRY=true
BUG=287377

Review URL: https://codereview.chromium.org/52413002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232061 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232061