Note that the second tap to bring up the handles and menu needs a ContextMenuAllowedScope. We'll need to add that to WebFrameWidgetImpl::HandleGestureEvent, similar to  crbug.com/795300 . However, that on it's own does not fix the issue with the initial selection.

Tap to select is a Contextual Search feature. I believe the selection is triggered in the browser. donnd@ might have more insight.

mcnee@ can you clarify?  When I tap on the text at the top of the page "Before you may cross..." the word is selected by the tap gesture.  Tapping on editable text fields is not supported by Contextual Search, and tapping on the text near those fields is problematic because of tap-gravity (the way taps near links try to select the link).

The "Before you may cross..." text at the top cannot be selected for me with --site-per-process, but it can be selected without --site-per-process.

As another example, visit http://csreis.github.io/tests/cross-site-iframe.html with --site-per-process

Tap the "Go cross-site (simple page)" button. The text cannot be selected with a tap.
Compare with the "Go same-site" option where the text can be selected with a tap.

To clarify the wording in c#4:
Tap the "Go cross-site (simple page)" button. The text inside the iframe "csreis.github.io" cannot be selected with a tap.
Compare with the "Go same-site" option where the text inside the iframe "Simple page" can be selected with a tap.

Thanks for the clarifications -- I simply didn't read the instructions in #1 well enough!  I can repro now.  I'm working to track down the failure, but there may be a solution in the pipeline already due to work to convert the messaging for this event to use Mojo.

Can you give us some very brief background on what the --site-per-process flag does and when you plan to roll out the feature?

See chromium.org/Home/chromium-security/site-isolation for details
As it concerns this bug, the cross-site iframe is rendered in a different process, which impacts the handling of input. Notably, a page may have multiple RenderWidgetHosts. In this case, in addition to the top level RenderWidgetHostViewAndroid, this page will have a RenderWidgetHostViewChildFrame.

I believe wjmaclean worked on issues related to touch selection with out-of-process iframes and may know more about this.

RE: when you plan to roll out the feature

AFAIK, there are no immediate plans to ship OOPIFs on Android (at least not in Q1 2018).

On Desktop (e.g. Windows, MacOs, Linux, CrOS) OOPIFs have shipped in M56 with --isolate-extensions feature and we expect to see an uptick in desktop users because of https://support.google.com/faqs/answer/7622138#chrome

Good to know this doesn't need to be fixed right away.  My work to use Mojo to communicate between Blink and the Browser should fix this (marking that as blocking this).