[PSA] bfcache Enabling bfcache by default on Desktop in M96

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Minoru Chikamune

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Oct 12, 2021, 1:33:40 AM10/12/21

to chromi...@chromium.org, embedd...@chromium.org, bfcac...@chromium.org, navigat...@chromium.org

tl;dr: We are enabling back/forward cache by default on Desktop in M96. This feature may require changes to Chromium embedder code.

Back/forward cache improves user experience by enabling instant history navigation to previously-visited pages by freezing and preserving them in memory and reusing them upon history navigations. This feature is now enabled by default. While the bfcache is implemented in //content, it changes a number of assumptions around navigation and document lifecycle, which can lead to various bugs in the code relying on them.

BFCache for a given WebContents is disabled unless the embedder explicitly opt-ins into it by overriding a IsBackForwardCacheSupported() method on WebContentsDelegate to return true. Given that instant history navigations considerably improve user experience, we encourage //content embedders to consider enabling it. However we strongly recommend //content embedders to audit their codebases to detect and fix assumptions invalidated by BFCache before enabling it — more details are available here.

Please feel free to reach out to the bfcac...@chromium.org if you have any questions about back/forward cache.