Expose Null ANGLE backend

ui/gl/gl_switches.cc

 // Copyright (c) 2012 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.
 
 #include "base/macros.h"
 #include "ui/gl/gl_switches.h"
 
 namespace gl {
 
 const char kGLImplementationDesktopName[]     = "desktop";
 const char kGLImplementationOSMesaName[]      = "osmesa";
 const char kGLImplementationAppleName[]       = "apple";
 const char kGLImplementationEGLName[]         = "egl";
 const char kGLImplementationANGLEName[]       = "angle";
 const char kGLImplementationSwiftShaderName[] = "swiftshader";
 const char kGLImplementationMockName[]        = "mock";
 
 const char kANGLEImplementationDefaultName[]  = "default";
 const char kANGLEImplementationD3D9Name[]     = "d3d9";
 const char kANGLEImplementationD3D11Name[]    = "d3d11";
 const char kANGLEImplementationOpenGLName[]   = "gl";
 const char kANGLEImplementationOpenGLESName[] = "gles";
+const char kANGLEImplementationNullName[]     = "null";
 
 }  // namespace gl
 
 namespace switches {
 
 // Disables use of D3D11.
 const char kDisableD3D11[]                  = "disable-d3d11";
 
 // Disables use of ES3 backend (use ES2 backend instead).
 const char kDisableES3GLContext[]           = "disable-es3-gl-context";
@@ skipping 85 matching lines @@
     kDisableGLDrawingForTests,
     kOverrideUseGLWithOSMesaForTests,
     kUseANGLE,
     kDisableDirectComposition,
     kEnableSwapBuffersWithDamage,
 };
 const int kGLSwitchesCopiedFromGpuProcessHostNumSwitches =
     arraysize(kGLSwitchesCopiedFromGpuProcessHost);
 
 }  // namespace switches