gpu: Mailbox emulation with EGLImage

ui/gl/gl_fence.h

Index: ui/gl/gl_fence.h
diff --git a/ui/gl/gl_fence.h b/ui/gl/gl_fence.h
index d4f3218d52f483947fce83a41c555aade3f92d54..c1967ec9c43df4666a17c56b6a6f7f84c45b5a98 100644
--- a/ui/gl/gl_fence.h
+++ b/ui/gl/gl_fence.h
@@ -16,8 +16,14 @@ class GL_EXPORT GLFence {
   virtual ~GLFence();
 
   static GLFence* Create();
+  // Creates a fence that is not guaranteed to signal until the current context
+  // is flushed. Use with caution.
+  static GLFence* CreateWithoutFlush();
   virtual bool HasCompleted() = 0;
   virtual void ClientWait() = 0;
+  // Will block the server if supported, but might fall back to blocking the
+  // client.
+  virtual void ServerWait() = 0;
 
  protected:
   static bool IsContextLost();