Style last updated text when data is stale.

The current text for when the data was last updated is a bit confusing. This
change alters the text to only give the time of the update: "Updated @ hh:mm".

The text will be colored as follows:
  * default style, if less than 5 minutes
  * orange, if at least 5 but less than 10 minutes,
  * red, if at least 10 but less than 20 minutes,
  * and black with red background, if 20 minutes or more.

I can animate the text for the 20 minutes+ case if you want, though I thought
making the background color red was garish enough to get noticed.

NOTRY=true
BUG=405247

Review URL: https://codereview.chromium.org/496773003

git-svn-id: svn://svn.chromium.org/blink/trunk@180729 bbb929c8-8fbe-4397-9dbb-9b2b20218538