Implement autoplay gesture override experiment.

public/web/WebSettings.h

Index: public/web/WebSettings.h
diff --git a/public/web/WebSettings.h b/public/web/WebSettings.h
index 9f012661ecb1bcfbcc79ddb9238ab8e389d7e872..9bfb306b00424d6095536dfffdb60d1cfd8d03dd 100644
--- a/public/web/WebSettings.h
+++ b/public/web/WebSettings.h
@@ -277,6 +277,7 @@ public:
     virtual void setWebSecurityEnabled(bool) = 0;
     virtual void setWideViewportQuirkEnabled(bool) = 0;
     virtual void setXSSAuditorEnabled(bool) = 0;
+    virtual void setAutoplayExperimentMode(const WebString&) = 0;

[dglazkov, 2015/08/06 20:55:23]

Let's not use a String here. Take a look at how TextTrackKindUserPreference is
used for an alternative.

[liberato (no reviews please), 2015/09/01 06:54:19]

I tried several approaches to make Settings.in take an enum, and they all have
some significant drawbacks.  TextTrackKindUserPreference is accessed from
outside blink as an enum, which isn't what i want.  i'd like to send in
human-readable strings, so that (e.g.) the finch experiment config doesn't have
experiment mode "3", but rather "enabled-ifviewport".  so, i need a string
parser somewhere, both for the tests and for outside WebKit.

however, i could find no single place to put the parser such that it can be
accessed both from outside blink and from the layout tests.  InternalSettings is
where TextTrack* adds a parser for the tests, but that's not going to help blink
consumers.  if there is some way have one parser implementation that both
about::flags and that blink layout tests could use, then that would make it all
work out.

so, after spending a fair bit of time trying to make it better, i moved back to
strings in the settings.  i did encapsulate the parsing in a separate helper
class, just to clean it up a little.

if i've missed some approach that avoids these issues, please let me know.

 
 protected:
     ~WebSettings() { }