Refactor fixed layout mode

Source/web/WebDevToolsAgentImpl.cpp

Index: Source/web/WebDevToolsAgentImpl.cpp
diff --git a/Source/web/WebDevToolsAgentImpl.cpp b/Source/web/WebDevToolsAgentImpl.cpp
index 5a76762c6a438ad67ea3a590fd4dc4e857632a7d..7767191ec5d0c3f9b50c9164d756e9b58d383963 100644
--- a/Source/web/WebDevToolsAgentImpl.cpp
+++ b/Source/web/WebDevToolsAgentImpl.cpp
@@ -332,9 +332,14 @@ private:
         int overrideWidth = effectiveEmulatedSize.width + scrollbarDimensions.width;
         int overrideHeight = effectiveEmulatedSize.height + scrollbarDimensions.height;
 
-        if (IntSize(overrideWidth, overrideHeight) != frameView->size())
+        if (IntSize(overrideWidth, overrideHeight) != frameView->size()) {
             frameView->resize(overrideWidth, overrideHeight);
 
+            // Since we're resizing the main-frame, we need to resize its layout size too since
+            // main frames' layout sizes are manually managed by WebViewImpl
+            frameView->setLayoutSize(IntSize(overrideWidth, overrideHeight));
+        }
+
         Document* doc = frameView->frame().document();
         doc->styleResolverChanged(RecalcStyleImmediately);
         doc->updateLayout();