Expand support in safe_numeric.h

* Refactor code in preparation for safe math operations.
* Support float type for numeric casts.
* Expose IsValueInRangeForNumericType as part of the API.
* Add saturated_cast.

BUG=332611
R=akalin@chromium.org, willchan@chromium.org

Review URL: https://codereview.chromium.org/131063002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245183 0039d316-1c4b-4281-b951-d872f2087c98

• base/base.gyp[diff]
• base/base.gypi[diff]
• base/safe_numerics.h[diff]
• base/safe_numerics_impl.h[Added - diff]
• base/safe_numerics_unittest.cc[diff]
• base/safe_numerics_unittest.nc[Deleted - diff]