blue to grey browser's progress bar

Change-Id: I7cabb70f84cd4f6c65a1c8b197831dad822498fa
Fix the problem that the favicons on the history page are shown ramdomly when the page is scrolled.

Steps to reproduce:
1. Visit some URLs to fill the history page.
2. Go to the history page.
3. Scroll up and down repeatedly.

What happened:
The favicons on the left side of the history page are shown ramdomly.

Change-Id: I243ec67899b13c5482e1503f7eab23dd9a5aa1f5
Signed-off-by: Sungmann Cho <sungmann.cho@navercorp.com>