Redo 38f3ee9 using a window...

... This seems the more portabe way to do it across platforms.  We are not
relying on a passed-in TrackPanel, for the sake of keeping TrackInfo
independent of TrackPanel.  We just get the active window from the
application, which should exists in all contexts in which the Settings are
demanded, which are drawing functions.

src/TrackInfo.cpp

@@ -32,7 +32,6 @@ Paul Licameli split from TrackPanel.cpp
 
 #include <wx/dc.h>
 #include <wx/frame.h>
-#include <wx/graphics.h>
 
 #include "AColor.h"
 #include "AllThemeResources.h"
@@ -49,10 +48,7 @@ struct Settings : PrefsListener {
    wxString gSoloPref;
    wxFont gFont;
 
-   Settings()
-   {
-      UpdatePrefs();
-   }
+   bool mInitialized{ false };
 
    void UpdatePrefs() override
    {
@@ -61,6 +57,13 @@ struct Settings : PrefsListener {
       // Calculation of best font size depends on language, so it should be redone in case
       // the language preference changed.
 
+      // wxWidgets seems to need a window to do this portably.
+      if ( !wxTheApp )
+         return;
+      auto window = wxTheApp->GetTopWindow();
+      if ( !window )
+         return;
+
       int fontSize = 10;
       gFont.Create(fontSize, wxFONTFAMILY_SWISS, wxFONTSTYLE_NORMAL, wxFONTWEIGHT_NORMAL);
 
@@ -69,24 +72,22 @@ struct Settings : PrefsListener {
          ( kTrackInfoWidth + kLeftMargin )
             - 2; // 2 to allow for left/right borders
       int textWidth;
-      std::unique_ptr<wxGraphicsContext> pContext(
-         wxGraphicsContext::Create()
-      );
-      pContext->SetFont( gFont, *wxBLACK );
       do {
          gFont.SetPointSize(fontSize);
-         double dWidth;
-         pContext->GetTextExtent(
-            _("Stereo, 999999Hz"), &dWidth, nullptr );
-         textWidth = (wxCoord)( dWidth + 0.5 );
+         window->GetTextExtent(_("Stereo, 999999Hz"),
+            &textWidth, nullptr, nullptr, nullptr, &gFont);
          fontSize--;
       } while (textWidth >= allowableWidth);
+
+      mInitialized = true;
    }
 };
 
 static Settings &settings()
 {
    static Settings theSettings;
+   if ( !theSettings.mInitialized )
+      theSettings.UpdatePrefs();
    return theSettings;
 }