DevTools: return error when trying to load an empty (0 x 0) picture

Source/core/inspector/InspectorLayerTreeAgent.cpp

 /*
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 349 matching lines @@
         }
         decodedTiles[i] = adoptRef(new PictureSnapshot::TilePictureStream());
         decodedTiles[i]->layerOffset.set(x, y);
         if (!base64Decode(picture, decodedTiles[i]->data)) {
             *errorString = "Invalid base64 encoding";
             return;
         }
     }
     RefPtr<PictureSnapshot> snapshot = PictureSnapshot::load(decodedTiles);
     if (!snapshot) {
-        *errorString = "Invalida snapshot format";
+        *errorString = "Invalid snapshot format";
         return;
     }
+    if (snapshot->isEmpty()) {
+        *errorString = "Empty snapshot";
+        return;
+    }
+
     *snapshotId = String::number(++s_lastSnapshotId);
     bool newEntry = m_snapshotById.add(*snapshotId, snapshot).isNewEntry;
     ASSERT_UNUSED(newEntry, newEntry);
 }
 
 void InspectorLayerTreeAgent::releaseSnapshot(ErrorString* errorString, const String& snapshotId)
 {
     SnapshotById::iterator it = m_snapshotById.find(snapshotId);
     if (it == m_snapshotById.end()) {
         *errorString = "Snapshot not found";
@@ skipping 76 matching lines @@
 void InspectorLayerTreeAgent::didRemovePageOverlay(const GraphicsLayer* layer)
 {
     size_t index = m_pageOverlayLayerIds.find(layer->platformLayer()->id());
     if (index == WTF::kNotFound)
         return;
     m_pageOverlayLayerIds.remove(index);
 }
 
 
 } // namespace blink