Introduce WebPageImportanceSignals to judge state preservation needs

Source/web/WebPageImportanceSignals.cpp

Index: Source/web/WebPageImportanceSignals.cpp
diff --git a/Source/web/WebPageImportanceSignals.cpp b/Source/web/WebPageImportanceSignals.cpp
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index 0000000000000000000000000000000000000000..b0e5de9a41abef1bfba6a63e6bfd671913fb27de
--- /dev/null
+++ b/Source/web/WebPageImportanceSignals.cpp
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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.
+
+#include "config.h"
+#include "public/web/WebPageImportanceSignals.h"
+
+#include "public/platform/Platform.h"
+
+namespace blink {
+
+void WebPageImportanceSignals::reset()
+{
+    m_hadFormInteraction = false;
+}
+
+void WebPageImportanceSignals::onCommitLoad()
+{
+    Platform::current()->histogramEnumeration("PageImportanceSignals.HadFormInteraction.OnCommitLoad", m_hadFormInteraction, 2);
+
+    reset();
+}
+
+} // namespace blink