Autoplay: use an autoplay policy setting in Blink.

third_party/WebKit/Source/core/testing/InternalSettings.idl

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 37 matching lines @@
     [RaisesException] void setViewportEnabled(boolean enabled);
     [RaisesException] void setViewportMetaEnabled(boolean enabled);
     [RaisesException] void setViewportStyle(DOMString style);
     [RaisesException] void setAvailablePointerTypes(DOMString pointers);
     [RaisesException] void setPrimaryPointerType(DOMString pointer);
     [RaisesException] void setAvailableHoverTypes(DOMString types);
     [RaisesException] void setPrimaryHoverType(DOMString type);
     [RaisesException] void setImageAnimationPolicy(DOMString policy);
     [RaisesException] void setCompositorWorkerEnabled(boolean enabled);
     [RaisesException] void setPresentationReceiver(boolean enabled);
+    [RaisesException] void setAutoplayPolicy(DOMString policy);
 
     // FIXME: The following are RuntimeEnabledFeatures and likely
     // cannot be changed after process start.  These setters should
     // be removed or moved onto internals.runtimeFlags:
     void setCSSStickyPositionEnabled(boolean enabled);
     void setLangAttributeAwareFormControlUIEnabled(boolean enabled);
     void setOverlayScrollbarsEnabled(boolean enabled);
     void setExperimentalContentSecurityPolicyFeaturesEnabled(boolean enabled);
     void setScrollTopLeftInteropEnabled(boolean enabled);
 };