Fix a bug in updating physical backing size

ui/android/view_android.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/android/view_android.h"
 
 #include <algorithm>
 
 #include "base/android/jni_android.h"
 #include "base/android/jni_string.h"
@@ skipping 108 matching lines @@
          children_.end());
   DCHECK(!RootPathHasEventForwarder(this) || !SubtreeHasEventForwarder(child))
       << "Some view tree path will have more than one event forwarder "
          "if the child is added.";
 
   // The new child goes to the top, which is the end of the list.
   children_.push_back(child);
   if (child->parent_)
     child->RemoveFromParent();
   child->parent_ = this;
-  child->OnPhysicalBackingSizeChanged(physical_size_);
+
+  // Empty physical backing size need not propagating down since it can
+  // accidentally overwrite the valid ones in the children.
+  if (!physical_size_.IsEmpty())
+    child->OnPhysicalBackingSizeChanged(physical_size_);
 }
 
 // static
 bool ViewAndroid::RootPathHasEventForwarder(ViewAndroid* view) {
   while (view) {
     if (view->has_event_forwarder())
       return true;
     view = view->parent_;
   }
 
@@ skipping 211 matching lines @@
         matched = bound.Contains(e->GetX(0), e->GetY(0));
       }
       if (matched && child->HitTest(send_to_client, *e))
         return true;
     }
   }
   return false;
 }
 
 }  // namespace ui