Refactor GL bindings so there is no global GLApi or DriverGL.

gpu/command_buffer/service/mailbox_manager_sync.cc

Index: gpu/command_buffer/service/mailbox_manager_sync.cc
diff --git a/gpu/command_buffer/service/mailbox_manager_sync.cc b/gpu/command_buffer/service/mailbox_manager_sync.cc
index 979700a19e38a321f608787bd54735a72b621501..dd9e6738818d53ca970815db9b34beccdcd2daec 100644
--- a/gpu/command_buffer/service/mailbox_manager_sync.cc
+++ b/gpu/command_buffer/service/mailbox_manager_sync.cc
@@ -38,7 +38,8 @@ base::LazyInstance<std::queue<SyncTokenToFenceMap::iterator>> g_sync_points =
 void CreateFenceLocked(const SyncToken& sync_token) {
 #if !defined(OS_MACOSX)
   g_lock.Get().AssertAcquired();
-  if (gl::GetGLImplementation() == gl::kGLImplementationMockGL)
+  if (gl::GetGLImplementation() == gl::kGLImplementationMockGL ||
+      gl::GetGLImplementation() == gl::kGLImplementationStubGL)
     return;
 
   std::queue<SyncTokenToFenceMap::iterator>& sync_points = g_sync_points.Get();