compositor-worker: cc->blink mutation plumbing

third_party/WebKit/Source/platform/graphics/CompositorMutatorClient.cpp

+// 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.
+
+#include "platform/graphics/CompositorMutatorClient.h"
+
+#include "base/bind.h"
+#include "base/callback.h"
+#include "platform/TraceEvent.h"
+#include "platform/graphics/CompositorMutation.h"
+#include "platform/graphics/CompositorMutationsTarget.h"
+
+namespace blink {
+
+CompositorMutatorClient::CompositorMutatorClient(CompositorMutationsTarget* mutationsTarget)
+    : m_mutationsTarget(mutationsTarget)
+    , m_mutations(nullptr)
+{
+    TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("compositor-worker"), "CompositorMutatorClient::CompositorMutatorClient");
+}
+
+CompositorMutatorClient::~CompositorMutatorClient()
+{
+    TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("compositor-worker"), "CompositorMutatorClient::~CompositorMutatorClient");
+}
+
+CompositorMutatorClient::ApplyMutationsCallback CompositorMutatorClient::TakeMutations()
+{
+    TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("compositor-worker"), "CompositorMutatorClient::TakeMutations");
+    if (!m_mutations)
+        return base::Closure();
+
+    return base::Bind(&CompositorMutationsTarget::applyMutations,

[esprehn, 2016/03/31 05:03:11]

What keeps m_mutationsTarget alive for this callback?

[majidvp, 2016/03/31 19:43:03]

It is kept alive by CompositorMutatorImpl (also owns CompositorMutatorClient)
which has the same lifetime as WebViewImpl. 
Here is the ownership chain: WebViewImpl <>-- CompositorMutatorImpl<>--
CompositorMutationTarget.

|CompositorMutatorImpl| will be in the follow-up patch, but that patch has not
been updated with most recent changes which
includes the introduction of the |CompositorMutationTarget|.

+        base::Unretained(m_mutationsTarget),
+        base::Owned(m_mutations.release().leakPtr()));
+}
+
+void CompositorMutatorClient::setMutationsForTesting(PassOwnPtr<CompositorMutations> mutations)
+{
+    m_mutations = mutations;
+}
+
+} // namespace blink