Refactor GL bindings so there is no global GLApi or DriverGL.

ui/gl/gl_context_stub.h

Index: ui/gl/gl_context_stub.h
diff --git a/ui/gl/gl_context_stub.h b/ui/gl/gl_context_stub.h
index d98927b2c5114edd08caf2d4cabcfb1443ba163f..7ddc3d1f02855ea7384b95243aef935435bac29b 100644
--- a/ui/gl/gl_context_stub.h
+++ b/ui/gl/gl_context_stub.h
@@ -27,12 +27,25 @@ class GL_EXPORT GLContextStub : public GLContextReal {
   bool IsCurrent(GLSurface* surface) override;
   void* GetHandle() override;
   void OnSetSwapInterval(int interval) override;
+  std::string GetGLVersion() override;
   std::string GetGLRenderer() override;
+  bool WasAllocatedUsingRobustnessExtension() override;
+  std::string GetExtensions() override;
+
+  void SetUseStubApi(bool stub_api);
+  void SetExtensionsString(const char* extensions);
+  void SetGLVersionString(const char* version_str);
 
  protected:
   ~GLContextStub() override;
 
+  GLApi* CreateGLApi(DriverGL* driver) override;
+
  private:
+  bool use_stub_api_;
+  std::string version_str_;
+  std::string extensions_;
+
   DISALLOW_COPY_AND_ASSIGN(GLContextStub);
 };