Introduce WebPageImportanceSignals to judge state preservation needs

public/web/WebPageImportanceSignals.h

Index: public/web/WebPageImportanceSignals.h
diff --git a/public/web/WebPageImportanceSignals.h b/public/web/WebPageImportanceSignals.h
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+++ b/public/web/WebPageImportanceSignals.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 WebPageImportanceSignals_h
+#define WebPageImportanceSignals_h
+
+#include "public/platform/WebCommon.h"
+
+namespace blink {
+
+// WebPageImportanceSignals indicate the importance of the page state to user.
+// This signal is propagated to embedder so that it can prioritize preserving
+// state of certain page over the others.
+class WebPageImportanceSignals {
+public:
+    WebPageImportanceSignals() { reset(); }
+
+    bool hadFormInteraction() const { return m_hadFormInteraction; }
+    void setHadFormInteraction() { m_hadFormInteraction = true; }
+
+    BLINK_EXPORT void reset();
+#if BLINK_IMPLEMENTATION
+    void onCommitLoad();
+#endif
+
+private:
+    bool m_hadFormInteraction : 1;
+};
+
+} // namespace blink
+
+#endif // WebPageImportancesignals_h