Revert "Implement StyleSheetCollectionForDocument and ShadowStyleSheetCollection."

This reverts https://src.chromium.org/viewvc/blink?revision=155768&view=revision
due to broken layout of Pica, the Polymer demo app.

Also reverts two followup fixes:
r155830: "DocumentStyleSheetCollection::removeStyleSheetCandidateNode should use scopingNode's treeScope."
r155835: "DocumentStyleSheetCollection::addStyleSheetCandidateNode should use node->treeScope for HTMLStyleElement."

BUG=244314,271078
TBR=tasak

Review URL: https://codereview.chromium.org/22380006

git-svn-id: svn://svn.chromium.org/blink/trunk@155887 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Make confidence interval calculation failures non-fatal.

This allows the HTML output of Telemetry and run-perf-tests to continue to
display even if the confidence interval cannot be calculated.

BUG=

Review URL: https://chromiumcodereview.appspot.com/22278006

git-svn-id: svn://svn.chromium.org/blink/trunk@155888 bbb929c8-8fbe-4397-9dbb-9b2b20218538