Honor --gpu-switching=force_discrete to always stay on discrete GPU.

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 "ui/gl/gl_switches.h"
 
 namespace gfx {
 
 const char kGLImplementationDesktopName[]     = "desktop";
 const char kGLImplementationOSMesaName[]      = "osmesa";
 const char kGLImplementationAppleName[]       = "apple";
 const char kGLImplementationEGLName[]         = "egl";
 const char kGLImplementationSwiftShaderName[] = "swiftshader";
 const char kGLImplementationMockName[]        = "mock";
 
 }  // namespace gfx
 
 namespace switches {
 
-// Disable dynamic switching between integrated and discrete GPU on
-// systems that would otherwise support it (currently, only a limited
-// number of MacBook Pros).
-const char kDisableGpuSwitching[]           = "disable-gpu-switching";
-
 // Stop the GPU from synchronizing on the vsync before presenting.
 const char kDisableGpuVsync[]               = "disable-gpu-vsync";
 
 // Turns on GPU logging (debug build only).
 const char kEnableGPUServiceLogging[]       = "enable-gpu-service-logging";
 const char kEnableGPUClientLogging[]        = "enable-gpu-client-logging";
 
 // Select which implementation of GL the GPU process should use. Options are:
 //  desktop: whatever desktop OpenGL the user has installed (Linux and Mac
 //           default).
@@ skipping 20 matching lines @@
 const char kGpuSwitchingOptionNameForceIntegrated[] = "force_integrated";
 const char kGpuSwitchingOptionNameForceDiscrete[]   = "force_discrete";
 const char kGpuSwitchingOptionNameAutomatic[]   = "automatic";
 
 // Flag used for Linux tests: for desktop GL bindings, try to load this GL
 // library first, but fall back to regular library if loading fails.
 const char kTestGLLib[]                     = "test-gl-lib";
 
 }  // namespace switches