Re-land: cc: Implement shared worker contexts.

content/renderer/gpu/mailbox_output_surface.cc

Index: content/renderer/gpu/mailbox_output_surface.cc
diff --git a/content/renderer/gpu/mailbox_output_surface.cc b/content/renderer/gpu/mailbox_output_surface.cc
index b7c3045bd5f783928bfcc916c0b535412f7952f7..fe6bd6aeb41c9fdf3e4995903f5c9a25029bab6d 100644
--- a/content/renderer/gpu/mailbox_output_surface.cc
+++ b/content/renderer/gpu/mailbox_output_surface.cc
@@ -43,7 +43,9 @@ MailboxOutputSurface::MailboxOutputSurface(
   capabilities_.uses_default_gl_framebuffer = false;
 }
 
-MailboxOutputSurface::~MailboxOutputSurface() {
+MailboxOutputSurface::~MailboxOutputSurface() {}
+
+void MailboxOutputSurface::DetachFromClient() {
   DiscardBackbuffer();
   while (!pending_textures_.empty()) {
     if (pending_textures_.front().texture_id) {
@@ -52,6 +54,7 @@ MailboxOutputSurface::~MailboxOutputSurface() {
     }
     pending_textures_.pop_front();
   }
+  cc::OutputSurface::DetachFromClient();
 }
 
 void MailboxOutputSurface::EnsureBackbuffer() {