Make GL calls go through subclassable class.

content/common/gpu/gpu_channel_manager.cc

Index: content/common/gpu/gpu_channel_manager.cc
diff --git a/content/common/gpu/gpu_channel_manager.cc b/content/common/gpu/gpu_channel_manager.cc
index d39736a078256d9f52913139b1b71f578d36b4fd..41a51c091c748097cbb1503d436d05df5c097380 100644
--- a/content/common/gpu/gpu_channel_manager.cc
+++ b/content/common/gpu/gpu_channel_manager.cc
@@ -58,7 +58,8 @@ GpuChannelManager::~GpuChannelManager() {
 
 gpu::gles2::ProgramCache* GpuChannelManager::program_cache() {
   if (!program_cache_.get() &&
-      (gfx::g_ARB_get_program_binary || gfx::g_OES_get_program_binary) &&
+      (gfx::g_driver_gl.ext.b_ARB_get_program_binary ||
+       gfx::g_driver_gl.ext.b_OES_get_program_binary) &&
       !CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kDisableGpuProgramCache)) {
     program_cache_.reset(new gpu::gles2::MemoryProgramCache());