Adding ThreadChecker validation to d'tors for client classes

remoting/ios/display/gl_demo_screen.mm

Index: remoting/ios/display/gl_demo_screen.mm
diff --git a/remoting/ios/display/gl_demo_screen.mm b/remoting/ios/display/gl_demo_screen.mm
index c293fe5cacabf1eae067c34957275cfaf1d15dec..738d1a67c048d731938d6d8a0f910c2ba9b500f7 100644
--- a/remoting/ios/display/gl_demo_screen.mm
+++ b/remoting/ios/display/gl_demo_screen.mm
@@ -35,7 +35,9 @@ const GLchar* a_position = "a_position";
 // integration. This will draw an expanding checkerboard pattern to the screen.
 GlDemoScreen::GlDemoScreen() : weak_factory_(this)  {}
 
-GlDemoScreen::~GlDemoScreen() {}
+GlDemoScreen::~GlDemoScreen() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+}
 
 void GlDemoScreen::SetCanvas(base::WeakPtr<Canvas> canvas) {
   canvas_ = canvas;