ui: Make the aura_demo not have solid colors in its layers.

This forces the compositor to use textures and allows us to verify the
texture upload path is working, instead of just testing solid color
layers work.

R=sadrul

Review URL: https://codereview.chromium.org/963303003

Cr-Commit-Position: refs/heads/master@{#318802}

ui/aura/demo/demo_main.cc

@@ -23,6 +23,7 @@
 #include "ui/events/event.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/geometry/rect.h"
+#include "ui/gfx/skia_util.h"
 #include "ui/gl/gl_surface.h"
 
 #if defined(USE_X11)
@@ -63,6 +64,14 @@ class DemoWindowDelegate : public aura::WindowDelegate {
   void OnCaptureLost() override {}
   void OnPaint(gfx::Canvas* canvas) override {
     canvas->DrawColor(color_, SkXfermode::kSrc_Mode);
+    gfx::Rect r;
+    canvas->GetClipBounds(&r);
+    // Fill with a non-solid color so that the compositor will exercise its
+    // texture upload path.
+    while (!r.IsEmpty()) {
+      r.Inset(2, 2);
+      canvas->FillRect(r, color_, SkXfermode::kXor_Mode);
+    }
   }
   void OnDeviceScaleFactorChanged(float device_scale_factor) override {}
   void OnWindowDestroying(aura::Window* window) override {}