public void insetContentRectByInternalMargins(int deltaLeft, int deltaTop, int deltaRight, int deltaBottom) {
        contentRectMinusAllMargins.left = contentRectMinusAllMargins.left + deltaLeft;
        contentRectMinusAllMargins.top = contentRectMinusAllMargins.top + deltaTop;
        contentRectMinusAllMargins.right = contentRectMinusAllMargins.right - deltaRight;
        contentRectMinusAllMargins.bottom = contentRectMinusAllMargins.bottom - deltaBottom;
    }
Calculates available width and height. Should be called when chart dimensions change. ContentRect is relative to
chart view not the device's screen.
hellocharts-library/src/lecho/lib/hellocharts/computator/ChartComputator.java