Fix 2 panel overflow related bugs on Windows.

Fix 2 panel overflow related bugs on Windows.
1) Bug 106880: Creating more than 6 overflow panels or closing the 6th overflow panel triggers assert on debug version
2) Bug 106882: Hovering the mouse over the top of the overflow panels may expand the overflow panels

BUG=106880, 106882
TEST=Manul test by following repro steps as in bugs

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=113663

[jennb, 2011-12-08 20:05:46]

LGTM

http://codereview.chromium.org/8885019/diff/1/chrome/browser/ui/panels/panel_...
File chrome/browser/ui/panels/panel_manager.cc (right):

http://codereview.chromium.org/8885019/diff/1/chrome/browser/ui/panels/panel_...
chrome/browser/ui/panels/panel_manager.cc:21: const int kOverflowStripThickness
= 26;
How is this change related to the bug fixes?

http://codereview.chromium.org/8885019/diff/1/chrome/browser/ui/panels/panel_...
File chrome/browser/ui/panels/panel_overflow_strip.cc (right):

http://codereview.chromium.org/8885019/diff/1/chrome/browser/ui/panels/panel_...
chrome/browser/ui/panels/panel_overflow_strip.cc:105: if (panels_.empty() ||
start_index == panels_.size())
Sufficient to just check start_index >= end_index?