Initializes WINDOWPLACEMENT::length in GetCroppedWindowRect.

BUG=https://code.google.com/p/webrtc/issues/detail?id=3196
R=sergeyu@chromium.org

Review URL: https://webrtc-codereview.appspot.com/21529004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@6213 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/modules/desktop_capture/win/window_capture_utils.cc b/modules/desktop_capture/win/window_capture_utils.cc
index c878a63..03e0219 100644
--- a/modules/desktop_capture/win/window_capture_utils.cc
+++ b/modules/desktop_capture/win/window_capture_utils.cc
@@ -21,6 +21,7 @@
     return false;
   }
   WINDOWPLACEMENT window_placement;
+  window_placement.length = sizeof(window_placement);
   if (!GetWindowPlacement(window, &window_placement)) {
     return false;
   }