Drop superfluous motions Assumes all pendingActions have the same (rounded) x-value.
function(opt_losslessOnly) {
    if (pendingActions.length <= 1) return;

    // Lossless compression: drop inconsequential moveTos.
    for (var i = pendingActions.length - 1; i > 0; i--) {
      var action = pendingActions[i];
      if (action[0] == MOVE_TO) {
        var prevAction = pendingActions[i - 1];
        if (prevAction[1] == action[1] && prevAction[2] == action[2]) {
          pendingActions.splice(i, 1);
        }
      }
    }

    // Lossless compression: ... drop consecutive moveTos ...
    for (var i = 0; i < pendingActions.length - 1; /* incremented internally */) {
      var action = pendingActions[i];
      if (action[0] == MOVE_TO && pendingActions[i + 1][0] == MOVE_TO) {
        pendingActions.splice(i, 1);
      } else {
        i++;
      }
    }

    // Lossy compression: ... drop all but the extreme y-values ...
    if (pendingActions.length > 2 && !opt_losslessOnly) {
      // keep an initial moveTo, but drop all others.
      var startIdx = 0;
      if (pendingActions[0][0] == MOVE_TO) startIdx++;
      var minIdx = null, maxIdx = null;
      for (var i = startIdx; i < pendingActions.length; i++) {
        var action = pendingActions[i];
        if (action[0] != LINE_TO) continue;
        if (minIdx === null && maxIdx === null) {
          minIdx = i;
          maxIdx = i;
        } else {
          var y = action[2];
          if (y < pendingActions[minIdx][2]) {
            minIdx = i;
          } else if (y > pendingActions[maxIdx][2]) {
            maxIdx = i;
          }
        }
      }
      var minAction = pendingActions[minIdx],
          maxAction = pendingActions[maxIdx];
      pendingActions.splice(startIdx, pendingActions.length - startIdx);
      if (minIdx < maxIdx) {
        pendingActions.push(minAction);
        pendingActions.push(maxAction);
      } else if (minIdx > maxIdx) {
        pendingActions.push(maxAction);
        pendingActions.push(minAction);
      } else {
        pendingActions.push(minAction);
      }
    }
  }