commit ac0330544bb3294a5df1aa94fb0cd7c896804e11
author wangxianzhu <wangxianzhu@chromium.org> Thu Jun 09 08:55:12 2016
committer Commit bot <commit-bot@chromium.org> Thu Jun 09 08:57:01 2016
tree 70b1ead1ecbcbf7f39a9ced3b892b3da2cabc6c0
parent dca471a13943862a41ac51e9561ea734b02ce8d8

WebScrollbarThemeClientImpl should not be DisplayItemClient

WebScrollbarThemeClientImpl inherited DisplayItemClient from
ScrollbarThemeClient but it is never used as a DisplayItemClient.

Let Scrollbar instead of ScrollbarThemeClient inherit
DisplayItemClient, and use Scrollbar type in ScrollbarTheme
paint methods.

This avoids the need to let WebScrollbarThemeClientImpl follow
the rules of DisplayItemClient caching.

Review-Url: https://codereview.chromium.org/2045963003
Cr-Commit-Position: refs/heads/master@{#398818}