Add 'u' to zoom stats display on high DPI devices

Still need to connect this to ImGui, but this is already useful

Bug: skia:
Change-Id: I925c7a9d6236cb2d865d45d6a68a5709bf2e3df7
Reviewed-on: https://skia-review.googlesource.com/143158
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/tools/viewer/Viewer.cpp b/tools/viewer/Viewer.cpp
index 8f1d7bb..b5a9084 100644
--- a/tools/viewer/Viewer.cpp
+++ b/tools/viewer/Viewer.cpp
@@ -183,6 +183,7 @@
     , fZoomWindowFixed(false)
     , fZoomWindowLocation{0.0f, 0.0f}
     , fLastImage(nullptr)
+    , fZoomUI(false)
     , fBackendType(sk_app::Window::kNativeGL_BackendType)
     , fColorMode(ColorMode::kLegacy)
     , fColorSpacePrimaries(gSrgbPrimaries)
@@ -480,6 +481,11 @@
         this->updateTitle();
         fWindow->inval();
     });
+    fCommands.addCommand('u', "GUI", "Zoom UI", [this]() {
+        fZoomUI = !fZoomUI;
+        fStatsLayer.setDisplayScale(fZoomUI ? 2.0f : 1.0f);
+        fWindow->inval();
+    });
 
     // set up slides
     this->initSlides();