Don't expect ack for ViewMsg_OnResize if backing size is empty

content/renderer/render_widget.cc

 // Copyright (c) 2012 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 "content/renderer/render_widget.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
@@ skipping 388 matching lines @@
     paint_aggregator_.ClearPendingUpdate();
 
     // When resizing, we want to wait to paint before ACK'ing the resize.  This
     // ensures that we only resize as fast as we can paint.  We only need to
     // send an ACK if we are resized to a non-empty rect.
     webwidget_->resize(new_size);
 
     // Resize should have caused an invalidation of the entire view.
     DCHECK(new_size.IsEmpty() || is_accelerated_compositing_active_ ||
            paint_aggregator_.HasPendingUpdate());
-  } else if (!RenderThreadImpl::current()->short_circuit_size_updates()) {
+  } else if (!RenderThreadImpl::current() ||  // Will be NULL during unit tests.
+             !RenderThreadImpl::current()->short_circuit_size_updates()) {
+    resize_ack = NO_RESIZE_ACK;
+  }
+
+  if (new_size.IsEmpty() || physical_backing_size.IsEmpty()) {
+    // For empty size or empty physical_backing_size, there is no next paint
+    // (along with which to send the ack) until they are set to non-empty.
     resize_ack = NO_RESIZE_ACK;
   }
 
   // Send the Resize_ACK flag once we paint again if requested.
-  if (resize_ack == SEND_RESIZE_ACK && !new_size.IsEmpty())
+  if (resize_ack == SEND_RESIZE_ACK)
     set_next_paint_is_resize_ack();
 
   if (fullscreen_change)
     DidToggleFullscreen();
 
   // If a resize ack is requested and it isn't set-up, then no more resizes will
   // come in and in general things will go wrong.
-  DCHECK(resize_ack != SEND_RESIZE_ACK || new_size.IsEmpty() ||
-         next_paint_is_resize_ack());
+  DCHECK(resize_ack != SEND_RESIZE_ACK || next_paint_is_resize_ack());
 }
 
 void RenderWidget::OnClose() {
   if (closing_)
     return;
   closing_ = true;
 
   // Browser correspondence is no longer needed at this point.
   if (routing_id_ != MSG_ROUTING_NONE) {
     RenderThread::Get()->RemoveRoute(routing_id_);
@@ skipping 1912 matching lines @@
 
   if (!context->Initialize(
           attributes,
           false /* bind generates resources */,
           CAUSE_FOR_GPU_LAUNCH_WEBGRAPHICSCONTEXT3DCOMMANDBUFFERIMPL_INITIALIZE))
     return NULL;
   return context.release();
 }
 
 }  // namespace content