Remove OSX-specific <meter> rendering.

Intent to Remove thread:!msg/blink-dev/T_soy0IYt7E/6gxId0IWEAAJ

This CL removes the following -webkit-appearance values, and change the default
<meter> rendering on OSX same as other platforms.

  - continuous-capacity-level-indicator
  - discrete-capacity-level-indicator
  - relevancy-level-indicator
  - rating-level-indicator

As the result, this CL removes LayoutMeter class, and it also removes all classes
in MeterShadowElements by moving element-specific code to HTMLMeterElement.


Review URL:

Cr-Commit-Position: refs/heads/master@{#378178}
47 files changed