chrome: Decide what to do with SetZoomLevel

[magreenblatt]

Original report by me.

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This issue involves the following functionality currently supported by the Alloy runtime:

• Zoom settings (SetZoomLevel; currently configurable via the Chrome UI).

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[magreenblatt]

• edited description

[magreenblatt]

See issue #2969 for background on the Chrome runtime.

[magreenblatt]

This would be chome::Zoom (which uses constants for zoom in/out/reset instead of taking a double value).

[magreenblatt]

We can call the functions from browser_commands.h:

bool CanZoomIn(content::WebContents* contents);
bool CanZoomOut(content::WebContents* contents);
bool CanResetZoom(content::WebContents* contents);
void Zoom(Browser* browser, content::PageZoom zoom);  // PAGE_ZOOM_OUT, PAGE_ZOOM_RESET, PAGE_ZOOM_IN

Unfortunately this doesn't align well with the existing SetZoomLevel/GetZoomLevel API.

[magreenblatt]

It looks like Chrome's ZoomController (used by the browser_commands functions) adds additional functionality on top of the content::HostZoomMap used by Alloy. ZoomController has SetZoomLevel/GetZoomLevel, so we could just call those methods directly.

The implementation of PageZoom::Zoom can be a useful reference for how Chrome expects these methods to be used. The interesting detail here is the clamping to preset zoom levels.

An API using constants (IDC_ZOOM_PLUS, IDC_ZOOM_NORMAL, IDC_ZOOM_MINUS) may also come with issue #3282.

Given how error-prone the SetZoomLevel/GetZoomLevel usage is currently (example), I would be in favor of deprecating/removing these methods in favor of the more explicit API used by browser_comments. To implement the same API for Alloy we would either borrow some of the Chrome implementation or potentially switch from HostZoomMap to ZoomController usage.

[magreenblatt]

Alloy we would either borrow some of the Chrome implementation or potentially switch from HostZoomMap to ZoomController usage.

Alloy already creates a ZoomController for extensions, so that should be fine to use here as well.

[magreenblatt]

For Chrome, it might also be good to expose configuration of ZoomController::SetShowsNotificationBubble (whether the zoom notification bubble can be shown when the zoom level is changed).