Description of Change

On Windows with multiple monitors at different DPI scaling, calling
BrowserWindow.setBounds() with coordinates on a different-DPI monitor
returns the wrong outer size. Requesting an 800×600 DIP window on a
1.375×/1.1× mixed-DPI setup currently returns ~734×550 DIP from getBounds().

Before fix — window visibly shrinks on the cross-DPI move:

After fix — outer matches the request within ±2 DIP (ScaleToEnclosingRect
rounding at non-integer DSFs):

Root cause

DesktopWindowTreeHostWin::SetBoundsInDIP converts the requested DIP rect to
pixels using the destination display's DSF, then ::SetWindowPos moves the
HWND. Windows fires WM_DPICHANGED synchronously during the move, and
HWNDMessageHandler::OnDpiChanged applies the OS-suggested lParam rect
verbatim — but Windows computed that rect as current_rect * new_dpi / old_dpi, so the already-destination-DPI-sized pixels we just sent get
rescaled by that ratio again, leaving the final outer off.

The mismatch is amplified by Windows 10+ text-scale: Chromium's
display::Display::device_scale_factor() folds the text-scale multiplier in
(1.25 × 1.10 = 1.375), but WM_DPICHANGED's wParam reports only the
display-DPI bucket (120, i.e. 1.25×). Any MulDiv-style cancellation
against Windows' DPI is therefore unsound.

Fix

Cache the destination-DPI pixel rect in SetBoundsInDIP just before
::SetWindowPos. OnDpiChanged substitutes the cached size for the
OS-suggested size; position still comes from lParam so the window lands
where Windows placed it. The cache is cleared right after
SetBoundsInPixels returns (WM_DPICHANGED is dispatched synchronously),
so it cannot leak into a later unrelated DPI change. No DPI math is
involved on purpose — passing through the already-correct pixel size
sidesteps the Chromium-DSF vs. Windows-DPI mismatch entirely.

See the patch commit message for the full analysis.

Checklist

• I have built and tested this change
• I have filled out the PR description
• I have reviewed and verified the changes
• npm test passes
• tests are added(https://github.com/electron/electron/blob/main/docs/development/testing.md)
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Fixed an issue where BrowserWindow.setBounds() returned the wrong size when targeting a monitor with a different DPI scaling than the window's current monitor on Windows.