Implement autoplay gesture override experiment.

Source/core/html/AutoplayExperimentConfig.cpp

+// 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 "core/html/AutoplayExperimentConfig.h"
+
+namespace blink {
+
+AutoplayExperimentConfig::Mode AutoplayExperimentConfig::fromString(const String& mode)
+{
+    AutoplayExperimentConfig::Mode value = AutoplayExperimentConfig::Mode::Off;
+    if (mode.contains("enabled"))
+        value |= AutoplayExperimentConfig::Mode::Enabled;
+    if (mode.contains("-ifviewport"))
+        value |= AutoplayExperimentConfig::Mode::IfViewport;
+    if (mode.contains("-ifmuted"))
+        value |= AutoplayExperimentConfig::Mode::IfMuted;
+    if (mode.contains("-ifmobile"))
+        value |= AutoplayExperimentConfig::Mode::IfMobile;
+    if (mode.contains("-playmuted"))
+        value |= AutoplayExperimentConfig::Mode::PlayMuted;
+
+    return value;
+}
+
+} // namespace blink