Set deviceScaleFactor on the renderer WebView to enable scaling when not in fixed-layout mode.

content/renderer/render_view_impl.cc

Index: content/renderer/render_view_impl.cc
diff --git a/content/renderer/render_view_impl.cc b/content/renderer/render_view_impl.cc
index 841f41c6d1d1c1a6f5dbfbc66325f7ad63d443eb..5d7e7f7158e96cd9092febc1a59aa2cb005520ff 100644
--- a/content/renderer/render_view_impl.cc
+++ b/content/renderer/render_view_impl.cc
@@ -2723,6 +2723,10 @@ void RenderViewImpl::ProcessViewLayoutFlags(const CommandLine& command_line) {
           base::StringToInt(tokens[1], &height))
         webview()->setFixedLayoutSize(WebSize(width,height));
     }
+  } else {
+    int device_scale = webkit_preferences_.default_device_scale_factor;
+    webview()->setDeviceScaleFactor(device_scale);
+    webview()->setPageScaleFactorLimits(1, WebKit::WebView::maxPageScaleFactor);
   }
 }