NetworkPanel: Overview: fix canvas size.
NetworkPanel: Overview: fix canvas size.

Network Overview is vertically blurred + extra padding seen on bottom.
This is because 1px bottom border is accounted as client area.

Moved bottom border to patent div to fix it.

BUG=

Review URL: https://codereview.chromium.org/1026023003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@192437 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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