cc: Make LayerTreeHostImpl unittests use a delegating output surface.

cc/test/test_gles2_interface.cc

Index: cc/test/test_gles2_interface.cc
diff --git a/cc/test/test_gles2_interface.cc b/cc/test/test_gles2_interface.cc
index c137c39450620ba78e768c48a6eb2ca2bef995d7..a8b27c2d0e41aec7826826bb6032ba9599ba1ee5 100644
--- a/cc/test/test_gles2_interface.cc
+++ b/cc/test/test_gles2_interface.cc
@@ -10,12 +10,8 @@
 
 namespace cc {
 
-TestGLES2Interface::TestGLES2Interface(TestWebGraphicsContext3D* test_context)
-    : test_context_(test_context) {
-  DCHECK(test_context_);
-}
-
-TestGLES2Interface::~TestGLES2Interface() {}
+TestGLES2Interface::TestGLES2Interface() = default;
+TestGLES2Interface::~TestGLES2Interface() = default;
 
 void TestGLES2Interface::GenTextures(GLsizei n, GLuint* textures) {
   for (GLsizei i = 0; i < n; ++i) {
@@ -400,4 +396,10 @@ GLenum TestGLES2Interface::GetGraphicsResetStatusKHR() {
   return GL_NO_ERROR;
 }
 
+void TestGLES2Interface::set_test_context(TestWebGraphicsContext3D* context) {
+  DCHECK(!test_context_);
+  test_context_ = context;
+  InitializeTestContext(test_context_);
+}
+
 }  // namespace cc