This CL migrates fast/replaced/available-height-for-content.html to
external/wpt/css/css-sizing/available-height-for-replaced-content.html.

Change-Id: Ife10bdaf02857ff5b4e4142e6354c7d002671c3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2320270
Commit-Queue: Oriol Brufau <[email protected]>
Reviewed-by: Manuel Rego <[email protected]>
Cr-Commit-Position: refs/heads/master@{#791872}