Simplify use of ContentDecryptionModuleResult with promises

Source/modules/encryptedmedia/ContentDecryptionModuleResultPromise.h

+// Copyright 2014 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 ContentDecryptionModuleResultPromise_h
+#define ContentDecryptionModuleResultPromise_h
+
+#include "bindings/core/v8/ScriptPromiseResolver.h"
+#include "core/dom/ExceptionCode.h"
+#include "platform/ContentDecryptionModuleResult.h"
+
+namespace blink {
+
+ExceptionCode WebCdmExceptionToExceptionCode(WebContentDecryptionModuleException);
+
+// This class wraps the promise resolver to simplify creation of
+// ContentDecryptionModuleResult objects, and is to be derived from to resolve

[ddorwin, 2014/11/11 22:44:09]

nit: s/derived from/subclassed/
That reads better.

[jrummell, 2014/11/11 23:30:10]

Done.

+// promises as needed. The default implementations of complete(),

[ddorwin, 2014/11/11 22:44:09]

I'm not sure what "resolve promises as needed" means, though. Maybe you mean to
say they should override one of the complete methods.

[jrummell, 2014/11/11 23:30:11]

Done.

+// completeWithSession(), etc. will reject the promise with an error.
+class ContentDecryptionModuleResultPromise : public ContentDecryptionModuleResult {

[ddorwin, 2014/11/11 22:44:09]

Why is this a "...ResultPromise"? It doesn't look like a promise and it actually
contains a promise.

[jrummell, 2014/11/11 23:30:11]

I guess ...ResultWithPromise would be better. However, the name is getting
longer and longer.

+public:
+    explicit ContentDecryptionModuleResultPromise(ScriptState*);

[ddorwin, 2014/11/11 22:44:09]

protected? Should this really be instantiated?

[jrummell, 2014/11/11 23:30:10]

Done.

+    virtual ~ContentDecryptionModuleResultPromise();
+
+    // ContentDecryptionModuleResult implementation.
+    virtual void complete() override;
+    virtual void completeWithSession(WebContentDecryptionModuleResult::SessionStatus) override;

[ddorwin, 2014/11/11 22:44:09]

Why does this "base class" have this specialized completion method? Why doesn't
it contain the others?

[jrummell, 2014/11/11 23:30:11]

ContentDecryptionModuleResult has 3 complete methods, and all are specified
here. The goal is to provide default implementations (that cause the promise to
be rejected) so that subclasses only need to override the complete method they
expect to get called.

+    virtual void completeWithError(WebContentDecryptionModuleException, unsigned long systemCode, const WebString&) final;
+
+    // It is only valid to call this before completion.
+    ScriptPromise promise();
+
+    virtual void trace(Visitor*);
+
+protected:
+    // Called when the promise is to be resolved by derived classes.

[ddorwin, 2014/11/11 22:44:09]

Resolves the promise with |value|. Used by subclasses to....

[jrummell, 2014/11/11 23:30:11]

Done.

+    template <typename... T>
+    void resolve(T... value)
+    {
+        m_resolver->resolve(value...);
+        m_resolver.clear();
+    }
+
+    // Reject the promise with a DOMException.

[ddorwin, 2014/11/11 22:44:09]

nit: Rejects

[jrummell, 2014/11/11 23:30:10]

Done.

+    void reject(ExceptionCode, const String& errorMessage);
+
+    ExecutionContext* executionContext() const;
+
+private:
+    RefPtr<ScriptPromiseResolver> m_resolver;
+};
+
+} // namespace blink
+
+#endif // ContentDecryptionModuleResultPromise_h