public function setStart($timeStamp = 0.0, $memoryBytes = 0)
	{
		if (!empty($this->points))
		{
			throw new \RuntimeException('The start point cannot be adjusted after points are added to the profiler.');
		}

		$this->startTimeStamp   = $timeStamp;
		$this->startMemoryBytes = $memoryBytes;

		$point = new ProfilePoint('start');

		// Store the point.
		$this->points[] = $point;

		// Add it in the lookup table.
		$this->lookup[$point->getName()] = \count($this->points) - 1;

		return $this;
	}