Set ColorChooserWin::current_color_chooser_ properly

      ColorChooserWin::current_color_chooser_ stays NULL, so ColorChooserWin::Open()
always creates new ColorChooserWin instance. In addition to this, the DCHECK() at
ColorChooserWin::OnColorChooserDialogClosed() that checks current_color_chooser_
always fails.

BUG=none

Review URL: https://chromiumcodereview.appspot.com/17174002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@206848 0039d316-1c4b-4281-b951-d872f2087c98