What is the smallest positive value of $a$ for which the line $x = a$ is a line of symmetry of the graph of $y = \sin \left( 2 x - \frac { 4 \pi } { 3 } \right)$ ?
A $\frac { \pi } { 12 }$
B $\frac { 5 \pi } { 12 }$
C $\quad \frac { 7 \pi } { 12 }$
D $\frac { 11 \pi } { 12 }$
E $\frac { 19 \pi } { 12 }$