[MD] Fix painting of attached bookmark bar (don't tile IDR_THEME_TOOLBAR).
[MD] Fix painting of attached bookmark bar (don't tile
IDR_THEME_TOOLBAR).

BUG=505807

Review URL: https://codereview.chromium.org/1530043002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#365628}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk