gpu: Bind dummy GL API when no context is current

ui/gl/gl_context.cc

Index: ui/gl/gl_context.cc
diff --git a/ui/gl/gl_context.cc b/ui/gl/gl_context.cc
index cd9a28c387dcfabd66c18b7ccf7bbd3b88c3ff44..6003dee17eaa2c7133705cde9ad5c55365ba5ca7 100644
--- a/ui/gl/gl_context.cc
+++ b/ui/gl/gl_context.cc
@@ -26,6 +26,25 @@ base::LazyInstance<base::ThreadLocalPointer<GLContext> >::Leaky
     current_real_context_ = LAZY_INSTANCE_INITIALIZER;
 }  // namespace
 
+GLContext::ScopedReleaseCurrent::ScopedReleaseCurrent(GLContext* context,
+                                                      GLSurface* surface)
+    : context_(context), surface_(surface) {
+  DCHECK(context && surface);
+  DCHECK(context->IsCurrent(surface));
+}
+
+GLContext::ScopedReleaseCurrent::~ScopedReleaseCurrent() {
+  if (surface_) {
+    DCHECK(context_);
+    context_->ReleaseCurrent(surface_);
+  }
+}
+
+void GLContext::ScopedReleaseCurrent::Release() {
+  context_ = NULL;
+  surface_ = NULL;
+}
+
 GLContext::GLContext(GLShareGroup* share_group) : share_group_(share_group) {
   if (!share_group_.get())
     share_group_ = new GLShareGroup;
@@ -125,6 +144,8 @@ GLContext* GLContext::GetRealCurrent() {
 void GLContext::SetCurrent(GLSurface* surface) {
   current_context_.Pointer()->Set(surface ? this : NULL);
   GLSurface::SetCurrent(surface);
+  if (!surface)
+    SetGLApiToNoContext();
 }
 
 GLStateRestorer* GLContext::GetGLStateRestorer() {