sw_engine shape: performance optimization.

sw_engine shape: performance optimization.

we introduced shared memory pool for avoiding reallocate memory
while it process the stroke outlines, It experimentally increase
the outline data if we use the allocated memory for multiples shape strokes,
we don't need to alloc/free memory during the process.

This shared outline memory is allocated for threads count
so that we don't interrupt memory access during the tasks.

@Issues: 75

Change-Id: I2794c4368e392fa774a5cf9a9fc771963427269a