TrackInfo doesn't use the kTopMargin or kBottomMargin constants...

... It only needs their sum, which it will assume is the constant amount of
padding always between tracks (not channels of a track).

(cherry picked from audacity commit 058c729ea544e326938b9473e7b9a5cd5ecc6ab5)

Signed-off-by: akleja <storspov@gmail.com>

src/TrackInfo.cpp

@@ -202,7 +202,7 @@ unsigned TrackInfo::MinimumTrackHeight()
       height += commonTrackTCPBottomLines.front().height;
    // + 1 prevents the top item from disappearing for want of enough space,
    // according to the rules in HideTopItem.
-   return height + kTopMargin + kBottomMargin + 1;
+   return height + kVerticalPadding + 1;
 }
 
 bool TrackInfo::HideTopItem( const wxRect &rect, const wxRect &subRect,
@@ -566,7 +566,7 @@ void TrackInfo::SetTrackInfoFont(wxDC * dc)
 unsigned TrackInfo::DefaultTrackHeight( const TCPLines &topLines )
 {
    int needed =
-      kTopMargin + kBottomMargin +
+      kVerticalPadding +
       totalTCPLines( topLines, true ) +
       totalTCPLines( commonTrackTCPBottomLines, false ) + 1;
    return (unsigned) std::max( needed, (int) TrackView::DefaultHeight );

src/ViewInfo.h

@@ -99,8 +99,9 @@ private:
 };
 
 // See big pictorial comment in TrackPanel.cpp for explanation of these numbers
+//! constants related to y coordinates in the track panel
 enum : int {
-   // constants related to y coordinates in the track panel
+   kVerticalPadding = 7, /*!< Width of padding below each channel group */
    kAffordancesAreaHeight = 20,
    kTopInset = 4,
    kTopMargin = kTopInset + kBorderThickness,
@@ -108,6 +109,8 @@ enum : int {
    kSeparatorThickness = kBottomMargin + kTopMargin,
 };
 
+static_assert( kVerticalPadding == kTopMargin + kBottomMargin );
+
 enum : int {
    kTrackInfoBtnSize = 18, // widely used dimension, usually height
    kTrackInfoSliderHeight = 25,