Implemented window class on linux. Standalone demos are working on linux now.

gpu/demos/framework/main_exe.cc

Index: gpu/demos/framework/main_exe.cc
===================================================================
--- gpu/demos/framework/main_exe.cc	(revision 37981)
+++ gpu/demos/framework/main_exe.cc	(working copy)
@@ -6,12 +6,20 @@
 #include "base/logging.h"
 #include "gpu/demos/framework/window.h"
 
+#if defined(OS_LINUX)
+#include <gtk/gtk.h>
+#endif  // OS_LINUX
+
 namespace {
 static const int kWindowWidth = 512;
 static const int kWindowHeight = 512;
 }  // namespace.
 
 int main(int argc, char *argv[]) {
+#if defined(OS_LINUX)
+  gtk_init(&argc, &argv);
+#endif  // OS_LINUX
+
   // AtExitManager is used by singleton classes to delete themselves when
   // the program terminates.
   base::AtExitManager at_exit_manager_;
@@ -22,3 +30,4 @@
   window.MainLoop();
   return EXIT_SUCCESS;
 }
+