Roll Observatory packages and add a roll script

packages/quiver/lib/src/async/metronome.dart

 // Copyright 2014 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
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   _tickDate() {
     // Hey now, what's all this hinky clock.now() calls? Simple, if the workers
     // on the receiving end of _controller.add() take a non-zero amount of time
     // to do their thing (e.g. rendering a large scene with canvas), the next
     // timer must be adjusted to account for the lapsed time.
     _controller.add(clock.now());
     _startTimer(clock.now());
   }
 }