A sequence of functions $f _ { 1 } , f _ { 2 } , f _ { 3 } , \ldots$ is defined by
$$\begin{aligned}
\mathrm { f } _ { 1 } ( x ) & = | x | \\
\mathrm { f } _ { n + 1 } ( x ) & = \left| \mathrm { f } _ { n } ( x ) + x \right| \quad \text { for } n \geq 1
\end{aligned}$$
Find the value of
$$\int _ { - 1 } ^ { 1 } \mathrm { f } _ { 99 } ( x ) \mathrm { d } x$$
A 0\\
B 0.5\\
C 1\\
D 49.5\\
E 50\\
F 99\\
G 99.5\\
H 100