add scale factor to set viewport for retina screenshots (#691)

* device scale

* fix node.js daemon

* fix cargo fmt formatting for scale factor code

* fixes

src/actions.ts

@@ -1465,11 +1465,33 @@ async function handleViewport(
   command: ViewportCommand,
   browser: BrowserManager
 ): Promise<Response> {
-  await browser.setViewport(command.width, command.height);
-  return successResponse(command.id, {
+  if (command.deviceScaleFactor && command.deviceScaleFactor !== 1) {
+    await browser.setViewport(command.width, command.height);
+    await browser.setDeviceScaleFactor(
+      command.deviceScaleFactor,
+      command.width,
+      command.height,
+      false
+    );
+  } else {
+    // deviceScaleFactor is 1 or undefined -- clear any previously-set CDP
+    // Emulation.setDeviceMetricsOverride so stale DPR doesn't persist.
+    try {
+      await browser.clearDeviceMetricsOverride();
+    } catch {
+      // Ignore if override was never set
+    }
+    await browser.setViewport(command.width, command.height);
+  }
+
+  const result: Record<string, unknown> = {
     width: command.width,
     height: command.height,
-  });
+  };
+  if (command.deviceScaleFactor !== undefined) {
+    result.deviceScaleFactor = command.deviceScaleFactor;
+  }
+  return successResponse(command.id, result);
 }
 
 async function handleUserAgent(