cc: Make LayerTreeHostImpl unittests use a delegating output surface.

cc/test/test_gles2_interface.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_TEST_TEST_GLES2_INTERFACE_H_
 #define CC_TEST_TEST_GLES2_INTERFACE_H_
 
 #include "gpu/command_buffer/client/gles2_interface_stub.h"
 
 namespace cc {
 class TestWebGraphicsContext3D;
 
 class TestGLES2Interface : public gpu::gles2::GLES2InterfaceStub {
  public:
-  explicit TestGLES2Interface(TestWebGraphicsContext3D* test_context);
+  TestGLES2Interface();
   ~TestGLES2Interface() override;
 
   void GenTextures(GLsizei n, GLuint* textures) override;
   void GenBuffers(GLsizei n, GLuint* buffers) override;
   void GenFramebuffers(GLsizei n, GLuint* framebuffers) override;
   void GenRenderbuffers(GLsizei n, GLuint* renderbuffers) override;
   void GenQueriesEXT(GLsizei n, GLuint* queries) override;
 
   void DeleteTextures(GLsizei n, const GLuint* textures) override;
   void DeleteBuffers(GLsizei n, const GLuint* buffers) override;
@@ skipping 129 matching lines @@
   GLuint CreateAndConsumeTextureCHROMIUM(GLenum target,
                                          const GLbyte* mailbox) override;
 
   void ResizeCHROMIUM(GLuint width,
                       GLuint height,
                       float device_scale,
                       GLboolean has_alpha) override;
   void LoseContextCHROMIUM(GLenum current, GLenum other) override;
   GLenum GetGraphicsResetStatusKHR() override;
 
- private:
-  TestWebGraphicsContext3D* test_context_;
+  void set_test_context(TestWebGraphicsContext3D* context);
+
+ protected:
+  virtual void InitializeTestContext(TestWebGraphicsContext3D* context) {}
+
+ protected:
+  TestWebGraphicsContext3D* test_context_ = nullptr;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_TEST_GLES2_INTERFACE_H_