Expose some sky_viewer plumbing to allow for reuse

sky/viewer/sky_viewer_base.h

Index: sky/viewer/sky_viewer_base.h
diff --git a/sky/viewer/sky_viewer_base.h b/sky/viewer/sky_viewer_base.h
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+// Copyright 2015 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 SKY_VIEWER_SKY_VIEWER_BASE_H_
+#define SKY_VIEWER_SKY_VIEWER_BASE_H_
+
+#include "mojo/common/tracing_impl.h"
+#include "mojo/icu/icu.h"
+#include "mojo/public/cpp/application/application_connection.h"
+#include "mojo/public/cpp/application/application_delegate.h"
+#include "mojo/public/cpp/application/application_impl.h"
+#include "mojo/public/cpp/application/interface_factory_impl.h"
+#include "mojo/services/content_handler/public/interfaces/content_handler.mojom.h"
+#include "sky/services/platform/platform_impl.h"
+
+namespace sky {
+
+// An abstract class that handles most of the details of setting up an
+// application that is intended to run Sky content. Subclasses must implement
+// the mojo::InterfaceFactory<mojo::ContentHandler>::Create() method to
+// specialize this class with the concrete content handler that they are using.
+class SkyViewerBase : public mojo::ApplicationDelegate,
+                      public mojo::InterfaceFactory<mojo::ContentHandler> {
+ public:
+  SkyViewerBase();
+
+  ~SkyViewerBase() override;
+
+ private:
+  // Overridden from ApplicationDelegate:
+  void Initialize(mojo::ApplicationImpl* app) override;
+
+  bool ConfigureIncomingConnection(
+      mojo::ApplicationConnection* connection) override;
+
+  scoped_ptr<PlatformImpl> platform_impl_;
+  mojo::TracingImpl tracing_;
+
+  DISALLOW_COPY_AND_ASSIGN(SkyViewerBase);
+};
+
+}  // namespace sky
+
+#endif  // SKY_VIEWER_SKY_VIEWER_BASE_H_