Implement SetViewContents in the client lib

mojo/services/native_viewport/native_viewport_win.cc

Index: mojo/services/native_viewport/native_viewport_win.cc
diff --git a/mojo/services/native_viewport/native_viewport_win.cc b/mojo/services/native_viewport/native_viewport_win.cc
index 86e7ce9a53e7c0186e8be2a2ac437613d1f8154b..84bfdc37f7cf1fccc56aa429baf484309cbe59cb 100644
--- a/mojo/services/native_viewport/native_viewport_win.cc
+++ b/mojo/services/native_viewport/native_viewport_win.cc
@@ -20,7 +20,14 @@ gfx::Rect GetWindowBoundsForClientBounds(DWORD style, DWORD ex_style,
   wr.right = bounds.x() + bounds.width();
   wr.bottom = bounds.y() + bounds.height();
   AdjustWindowRectEx(&wr, style, FALSE, ex_style);
-  return gfx::Rect(wr.left, wr.top, wr.right - wr.left, wr.bottom - wr.top);
+
+  // Make sure to keep the window onscreen, as AdjustWindowRectEx() may have
+  // moved part of it offscreen.
+  gfx::Rect window_bounds(wr.left, wr.top,
+                          wr.right - wr.left, wr.bottom - wr.top);
+  window_bounds.set_x(std::max(0, window_bounds.x()));
+  window_bounds.set_y(std::max(0, window_bounds.y()));
+  return window_bounds;
 }
 
 }