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

ui/gl/init/gl_initializer_win.cc

Index: ui/gl/init/gl_initializer_win.cc
diff --git a/ui/gl/init/gl_initializer_win.cc b/ui/gl/init/gl_initializer_win.cc
index 89a3586dc1cf313b4b0d9624f4d2166c8375ce3a..6116bfbd9a4b604ec2c5f0e8f80fd04fd9d0c386 100644
--- a/ui/gl/init/gl_initializer_win.cc
+++ b/ui/gl/init/gl_initializer_win.cc
@@ -250,6 +250,7 @@ bool InitializeGLOneOffPlatform() {
       break;
     case kGLImplementationOSMesaGL:
     case kGLImplementationMockGL:
+    case kGLImplementationStubGL:
       break;
     default:
       NOTREACHED();
@@ -277,7 +278,8 @@ bool InitializeStaticGLBindings(GLImplementation implementation) {
     case kGLImplementationDesktopGL:
       return InitializeStaticWGLInternal();
     case kGLImplementationMockGL:
-      SetGLImplementation(kGLImplementationMockGL);
+    case kGLImplementationStubGL:
+      SetGLImplementation(implementation);
       InitializeStaticGLBindingsGL();
       return true;
     default: