feat: implement two-finger swipe navigation support for macOS

[devin-ai-integration]

Two-Finger Swipe Navigation Support for macOS

This PR implements support for two-finger swipe navigation in Electron for macOS as an opt-in feature, addressing GitHub issue electron#2683.

Changes Made

WebPreferences Integration

• Added enableTwoFingerSwipe boolean option to WebPreferences (disabled by default)
• Added constant kEnableTwoFingerSwipe in options_switches.h
• Extended WebContentsPreferences class with parsing logic and getter method
• Updated documentation in web-preferences.md

Swipe Detection Implementation

• Modified swiz_nsview_swipeWithEvent method in electron_ns_window.mm to detect both two-finger and three-finger swipes
• Added logic to differentiate between gesture types using NSEvent phase information and delta values
• Implemented ShouldEnableTwoFingerSwipe() method in NativeWindowMac to check WebPreferences setting
• Integrated WebPreferences check into swipe handling logic

Key Features

• Opt-in behavior: Feature is disabled by default and must be explicitly enabled via WebPreferences
• Backward compatibility: Existing three-finger swipe functionality remains unchanged
• Proper integration: Uses existing swipe event infrastructure and NativeWindow observer pattern
• WebPreferences approach: Configuration through WebPreferences instead of BrowserWindow options as requested

Usage

const { BrowserWindow } = require('electron')

const win = new BrowserWindow({
  webPreferences: {
    enableTwoFingerSwipe: true  // Enable two-finger swipe navigation
  }
})

// Listen for swipe events
win.on('swipe', (event, direction) => {
  console.log('Swipe detected:', direction) // 'left', 'right', 'up', 'down'
})

Technical Implementation

The implementation follows Electron's existing architecture:

1. WebPreferences Layer: New option parsed and stored in WebContentsPreferences
2. Native Layer: NativeWindowMac checks preference setting via ShouldEnableTwoFingerSwipe()
3. Cocoa Layer: Enhanced swipe detection in electron_ns_window.mm with preference validation
4. Event Layer: Reuses existing NotifyWindowSwipe infrastructure

Testing

The implementation has been tested to ensure:

• Two-finger swipes are detected when enabled via WebPreferences
• Three-finger swipes continue to work as before
• Feature is properly disabled by default (opt-in behavior)
• WebPreferences setting correctly enables/disables the feature

Files Modified

• shell/common/options_switches.h - Added kEnableTwoFingerSwipe constant
• shell/browser/web_contents_preferences.h - Added member variable and getter
• shell/browser/web_contents_preferences.cc - Added parsing logic and initialization
• shell/browser/native_window_mac.h - Added ShouldEnableTwoFingerSwipe method declaration
• shell/browser/native_window_mac.mm - Implemented preference checking method
• shell/browser/ui/cocoa/electron_ns_window.mm - Enhanced swipe detection logic
• docs/api/structures/web-preferences.md - Added documentation

---

Link to Devin run: https://app.devin.ai/sessions/5ef9e74c0a8844b383c4f93cab5f2fb9
Requested by: Evan (evan@iamevan.dev)

Addresses electron#2683

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[IAmStiven]

cool

[devin-ai-integration]

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