Add OpenGL support to Linux viewer

tools/viewer/sk_app/unix/Window_unix.h

 /*
 * Copyright 2016 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
 
 #ifndef Window_unix_DEFINED
 #define Window_unix_DEFINED
 
 #include <X11/Xlib.h>
+#include <GL/glx.h>
 #include "../Window.h"
 #include "SkChecksum.h"
 #include "SkTDynamicHash.h"
 
 typedef Window XWindow;
 
 namespace sk_app {
 
 struct ContextPlatformData_unix {
-    Display* fDisplay;
-    XWindow  fHWnd;
-    VisualID fVisualID;
+    Display*     fDisplay;
+    XWindow      fWindow;
+    XVisualInfo* fVisualInfo;
 };
 
 class Window_unix : public Window {
 public:
-    Window_unix() : Window() {}
-    ~Window_unix() override {}
+    Window_unix() : Window()
+                  , fDisplay(nullptr)
+                  , fWindow(0)
+                  , fGC(nullptr)
+                  , fVisualInfo(nullptr)
+                  , fMSAASampleCount(0) {}
+    ~Window_unix() override { this->closeWindow(); }
 
-    bool init(Display* display);
+    bool initWindow(Display* display, const DisplayParams* params);
 
     void setTitle(const char*) override;
     void show() override;
 
     bool attach(BackendType attachType, const DisplayParams& params) override;
 
     void onInval() override;
 
     bool handleEvent(const XEvent& event);
 
     static const XWindow& GetKey(const Window_unix& w) {
-        return w.fHWnd;
+        return w.fWindow;
     }
 
     static uint32_t Hash(const XWindow& w) {
         return SkChecksum::Mix(w);
     }
 
     static SkTDynamicHash<Window_unix, XWindow> gWindowMap;
 
     void markPendingPaint() { fPendingPaint = true; }
     void finishPaint() { 
         if (fPendingPaint) {
             this->onPaint(); 
             fPendingPaint = false; 
         }
     }
 
     void markPendingResize(int width, int height) { 
         fPendingWidth = width; 
         fPendingHeight = height;
         fPendingResize = true;
     }
     void finishResize() { 
         if (fPendingResize) {
             this->onResize(fPendingWidth, fPendingHeight); 
             fPendingResize = false;
         } 
     }
 
 private:
-    Display* fDisplay;
-    XWindow  fHWnd;
+    void closeWindow();
+
+    Display*     fDisplay;
+    XWindow      fWindow;
+    GC           fGC;
+    XVisualInfo* fVisualInfo;
+    int          fMSAASampleCount;
 
     Atom     fWmDeleteMessage;
 
     bool     fPendingPaint;
     int      fPendingWidth;
     int      fPendingHeight;
     bool     fPendingResize;
 };
 
 }   // namespace sk_app
 
 #endif