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

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

Index: third_party/WebKit/public/platform/callback/WebClosure.h
diff --git a/third_party/WebKit/public/platform/callback/WebClosure.h b/third_party/WebKit/public/platform/callback/WebClosure.h
new file mode 100644
index 0000000000000000000000000000000000000000..b85a23efa8dccb53f415510270d1f78d904ebce0
--- /dev/null
+++ b/third_party/WebKit/public/platform/callback/WebClosure.h
@@ -0,0 +1,72 @@
+// 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)
+    {
+        m_closure = base::Bind(&RunAndDelete, 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;
+        other.m_haveClosure = false;

[esprehn, 2016/03/25 01:05:06]

ditto, guard the m_haveClosure code with debug ifdef

[danakj, 2016/03/25 01:41:53]

Done.

+        m_closure = std::move(other.m_closure);
+        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:
+#if BLINK_IMPLEMENTATION
+    static void RunAndDelete(scoped_ptr<SameThreadClosure> c) { (*c)(); }
+#endif
+
+    bool m_haveClosure = true;

[esprehn, 2016/03/25 01:05:05]

ifdef this to debug only, the boolean is only used for asserts.

[danakj, 2016/03/25 01:41:53]

Done, to DCHECK_IS_ON().

+    base::Closure m_closure;
+
+    DISALLOW_COPY_AND_ASSIGN(WebClosure);
+};
+
+} // namespace blink
+
+#endif // WebClosure_h