Add a flag to require a user gesture to add an entry to the back/forward list.

third_party/WebKit/Source/core/frame/Settings.in

 # Defines properties which are available on the Settings object.
 #
 # Please think carefully before adding a new Setting.  Some questions to
 # consider are:
 # - Should this be a RuntimeEnabledFeature instead? Settings are for things
 #   which we support either values of at runtime.  Features are set at renderer
 #   process startup and are never changed. Features also tend to be set to a
 #   value based on the platform or the stability of the code in question, where
 #   as settings both codepaths need to be stable.
 # - How will you ensure test coverage of all relevant values of your setting?
@@ skipping 351 matching lines @@
 textTrackTextSize type=String
 
 # Margin for title-safe placement of cues with overscan, gives top and bottom margin size as
 # percentage of video element height (for horizontal text) into which cues will not be placed.
 textTrackMarginPercentage type=double, initial=0
 
 lowPriorityIframes initial=false
 
 progressBarCompletion type=ProgressBarCompletion, initial=ProgressBarCompletion::LoadEvent
 
+historyEntryRequiresUserGesture initial=false
+
 # Do we want to try to save screen real estate in the media player by hiding
 # the volume slider / mute button?
 preferHiddenVolumeControls initial=false
 
 # Whether to disallow network fetches for parser blocking scripts in the main
 # frame inserted via document.write, for users on slow connections.
 disallowFetchForDocWrittenScriptsInMainFrameOnSlowConnections initial=false
 
 # Whether to disallow network fetches for parser blocking scripts in the main
 # frame inserted via document.write, regardless of connection type.
@@ skipping 28 matching lines @@
 # Variant of the ParseHTMLOnMainThread experiment. This is designed to coalesce
 # TokenizedChunks when the experiment is running in threaded mode.
 parseHTMLOnMainThreadCoalesceChunks initial=false
 
 # Whether the CSSPreloadScanner is used for externally CSS preloads. NoPreload
 # indicates that the scanner will be used, but no preloads issued.
 cssExternalScannerNoPreload initial=false
 cssExternalScannerPreload initial=false
 
 browserSideNavigationEnabled initial=false