bindBuffer(buffer) {
    const gl = this.gl_;
    const bufferKey = getUid(buffer);
    let bufferCache = this.bufferCache_[bufferKey];
    if (!bufferCache) {
      const webGlBuffer = gl.createBuffer();
      bufferCache = {
        buffer: buffer,
        webGlBuffer: webGlBuffer,
      };
      this.bufferCache_[bufferKey] = bufferCache;
    }
    gl.bindBuffer(buffer.getType(), bufferCache.webGlBuffer);
  }
Just bind the buffer if it's in the cache. Otherwise create
the WebGL buffer, bind it, populate it, and add an entry to
the cache.
@param {import("./Buffer").default} buffer Buffer.