The latest stable release of Chromium for Android (73.0.3683.75) adds the android_64bit_browser build option for using 64-bit browser and WebView processes in Monochrome builds. They aren't using it themselves at the moment but it replaces the need for my 64-bit Monochrome patch.
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My tiny patch for using 64-bit WebView processes with the standalone WebView is still necessary (github.com/AndroidHardeni), but that's easy to maintain compared to the somewhat less trivial patch for Monochrome which needed adjustments for most releases:
github.com/AndroidHardeni
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AndroidHardening uses Monochrome to provide both the Chromium browser and WebView from the same app. It maps the same shared object and other components from the apk for both frontends. This substantially cuts down build time, storage and memory usage compared to separate apps.
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Using 64-bit processes provides much more than just high entropy ASLR and canaries. It's required by github.com/AndroidHardeni and will be needed for ARMv8.3 pointer auth along with ARMv8.5 memory tagging and Branch Target Indicators (coarse CFI). 32-bit will be purged soon enough.
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They used these 32-bit process as a memory optimization, which is no longer going to be possible on pure 64-bit devices (android-developers.googleblog.com/2019/01/get-yo). The memory optimization only became possible for the WebView once it started using sandboxed renderers. 64-bit was always supported.
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