Fix problems with absolute value function.

Fix problems with absolute value function.

The standard library provides seven absolute value functions.  From C,
there is abs, labs, llabs, fabs, fabsf, and fabsl for the types int,
long, long long, double, float and long double.  Due to numeric
conversions, these functions can accept arguments of any numeric types,
silently converting between types.  C++ libraries has std::abs, which
provides overloads for all these types, making it a better choice.  The
following problems have been observed, along with their fixes:

1) The wrong sized absolute value was used.  Using abs for a long long
would cause a cast to int first, resulting in unexpected values outside
of the range (INT_MIN, INT_MAX).  Switch to using std::abs
2) Using the wrong type of absolute value function.  Passing a floating
point number to an integer absolute value will cause rounding of
values, especially important for values close to zero.  Switch to using
std::abs
3) Taking the absolute value of an unsigned value.  This usually has no
effect, but may have some effects from casting.  Fixed by removing the
absolute value function.
4) Attempting to find the absolute difference between two unsigned
values.  These were transformed from abs(a - b) to
(a > b ? a - b : b - a).  This ternary expression is usually stored in
another variable.
5) Accidentally capturing the conditional such as
abs(a - b < threshold).  Moving the parentheses over to fix.
6) Some static_casts were used to, such as from uint32 -> int64, to get
a signed value in the absolute value.
7) A few types were changed from unsigned to signed.

Merge internal change: 61013787

R=rch@chromium.org

[Ryan Hamilton, 2014-02-08 01:32:20]

lgtm