Revert of Make the Sk GL context class an abstract base class

include/gpu/gl/SkANGLEGLContext.h

Index: include/gpu/gl/SkANGLEGLContext.h
diff --git a/include/gpu/gl/SkANGLEGLContext.h b/include/gpu/gl/SkANGLEGLContext.h
index 18cdbdb213a71ae6a7c579d9e66e8654ce1dd1a9..c5f62ff3ce85461a50305155f9c438bea700049d 100644
--- a/include/gpu/gl/SkANGLEGLContext.h
+++ b/include/gpu/gl/SkANGLEGLContext.h
@@ -10,12 +10,12 @@
 
 #if SK_ANGLE
 
-#include "SkGLContext.h"
+#include "SkGLContextHelper.h"
 
 #include <GLES2/gl2.h>
 #include <EGL/egl.h>
 
-class SkANGLEGLContext : public SkGLContext {
+class SkANGLEGLContext : public SkGLContextHelper {
 public:
     SkANGLEGLContext();
 
@@ -23,6 +23,17 @@
 
     virtual void makeCurrent() const SK_OVERRIDE;
     virtual void swapBuffers() const SK_OVERRIDE;
+
+    class AutoContextRestore {
+    public:
+        AutoContextRestore();
+        ~AutoContextRestore();
+
+    private:
+        EGLContext fOldEGLContext;
+        EGLDisplay fOldDisplay;
+        EGLSurface fOldSurface;
+    };
 
 protected:
     virtual const GrGLInterface* createGLContext(