Make lost context callback a base::Closure thru the WGC3DProvider.

third_party/WebKit/public/platform/callback/WebClosure.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef WebClosure_h
+#define WebClosure_h
+
+#include "base/bind.h"
+#include "base/callback.h"
+#include "base/callback_helpers.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "public/platform/WebCommon.h"
+
+#include <utility>
+
+#if BLINK_IMPLEMENTATION
+#include "wtf/Functional.h"
+#else
+#include "base/logging.h"
+#endif
+
+namespace blink {
+
+// Conversion from WTF closures to base closures to pass a callback out of blink.
+class WebClosure {
+public:
+#if BLINK_IMPLEMENTATION
+    WebClosure() {}
+
+    explicit WebClosure(PassOwnPtr<SameThreadClosure> c)
+    {
+        auto run_and_delete = +[](scoped_ptr<SameThreadClosure> c)
+        {
+            (*c)();
+        };
+        m_closure = base::Bind(run_and_delete, base::Passed(make_scoped_ptr(c.leakPtr())));
+    }
+#endif
+
+    // TODO(danakj): These could be =default with MSVC 2015.
+    WebClosure(WebClosure&& other) { *this = std::move(other); }
+    WebClosure& operator=(WebClosure&& other)
+    {
+        m_haveClosure = other.m_haveClosure;

[dcheng, 2016/03/24 15:53:56]

Should m_have closure be set to false?

[danakj, 2016/03/24 17:53:51]

But what if the |other| had a closure, now this one does?

[dcheng, 2016/03/24 18:00:18]

Sorry, to clarify, I meant other.m_haveClosure should become false.

[danakj, 2016/03/24 18:03:16]

Oh oh ok!

+        m_closure = base::ResetAndReturn(&other.m_closure);

[dcheng, 2016/03/24 15:53:56]

std::move() this too?

[danakj, 2016/03/24 17:53:51]

But it's an rvalue no?

[dcheng, 2016/03/24 18:00:18]

Not sure what you mean. I believe that
  m_closure = std::move(other.m_closure);
should be equivalent to what's currently written, no?

[danakj, 2016/03/24 18:03:16]

OOh, I see. Does callback null itself when you move from it? I figured it
didn't. *reads*

[danakj, 2016/03/24 18:06:04]

It totes does. Done.

+        return *this;
+    }
+
+#if !BLINK_IMPLEMENTATION
+    // TODO(danakj): This could be rvalue-ref-qualified.
+    base::Closure ToBaseClosure()
+    {
+        // Don't call this more than once!
+        DCHECK(m_haveClosure);
+        m_haveClosure = false;
+        return std::move(m_closure);
+    }
+#endif
+
+private:
+    bool m_haveClosure = true;
+    base::Closure m_closure;
+
+    DISALLOW_COPY_AND_ASSIGN(WebClosure);
+};
+
+} // namespace blink
+
+#endif // WebClosure_h