[omartelo]

Fixes TestChromeAPaneOpenedOnADialogShowsThePage on macos-15-intel, which failed the v0.81.0 release job (run 40757293299).

Root cause

A product bug, not only a test bug. Up to Chrome 153, Page.startScreencast and Page.stopScreencast return FallThrough in content/browser/devtools/protocol/page_handler.cc, so Chrome answers them only once the renderer has seen them. A renderer holding a JavaScript dialog sees nothing until the dialog closes, although the browser has already started or stopped the frames. Chrome 154 answers both from the browser (Response::Success()). macos-15-intel ships Chrome 151 and macos-latest ships 155/156, which is why only the Intel release job failed.

The impact: with Chrome 153 or older, on any OS, opening the browser pane on a page holding a dialog waited the whole pageWait (30 s) in Attach, which then dropped the session's browser. A probe on the runner showed Page.stopScreencast blocked until the dialog was answered in 16 of 16 runs, while browser-level and browser-handled page commands answered in about 1 ms.

The test asserted what the contract promises and is unchanged.

Fix

• chrome_view.go: screencast starts and stops run in order on a queue (castPastDialog) and return once done or once the page holds a dialog; the step runs on after that, and an error it meets later is logged. A stop is sent only while a screencast runs, so a pane opened on a held page starts its frames without a stop waiting first.
• dialogs_test.go: a unit test with a step that blocks the way Chrome 151's reply does: the caller returns under the dialog and the steps run in order.
• docs/ceilings.md: on Chrome 153 and older, a pane resized while a dialog is open keeps its last frame until the dialog is answered.

No CHANGELOG entry: dialogs ship in 0.81.0, which has not been released yet.

Measurement (GitHub runners, go test -v -count=N)

Runner	Suite	Before	After (2 runs)
macos-15-intel, Chrome 151	pane test	3/20 failed	0/50, 0/50
macos-15-intel	-run TestChrome	1 failure in 3 rounds	0/125, 0/125
macos-latest, Chrome 155/156	pane test	0/20	0/50, 0/50
macos-latest	-run TestChrome	0/75	0/125, 0/125

Test plan

• Local gate: gofmt -l ., go vet ./..., go test ./...
• go test -race -count=200 -run TestAScreencastUnderADialog ./internal/browser/
• macOS measurement above (temporary job removed in the last commit)