resources: Prevent including the same resource in multiple pack files.

ui/base/resource/data_pack.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 "ui/base/resource/data_pack.h"
 
 #include <errno.h>
 
 #include "base/files/file_util.h"
 #include "base/files/memory_mapped_file.h"
@@ skipping 213 matching lines @@
 }
 
 ResourceHandle::TextEncodingType DataPack::GetTextEncodingType() const {
   return text_encoding_type_;
 }
 
 ui::ScaleFactor DataPack::GetScaleFactor() const {
   return scale_factor_;
 }
 
+#if DCHECK_IS_ON()
+void DataPack::CheckForDuplicateResources(
+    const ScopedVector<ResourceHandle>& packs) {
+  for (size_t i = 0; i < resource_count_ + 1; ++i) {
+    const DataPackEntry* entry = reinterpret_cast<const DataPackEntry*>(
+        mmap_->data() + kHeaderLength + (i * sizeof(DataPackEntry)));
+    const uint16 resource_id = entry->resource_id;
+    const float resource_scale = GetScaleForScaleFactor(scale_factor_);
+    for (const ResourceHandle* handle : packs) {
+      DCHECK_IMPLIES(
+          GetScaleForScaleFactor(handle->GetScaleFactor()) == resource_scale,
+          !handle->HasResource(resource_id));
+    }
+  }
+}
+#endif  // DCHECK_IS_ON()
+
 // static
 bool DataPack::WritePack(const base::FilePath& path,
                          const std::map<uint16, base::StringPiece>& resources,
                          TextEncodingType textEncodingType) {
   FILE* file = base::OpenFile(path, "wb");
   if (!file)
     return false;
 
   if (fwrite(&kFileFormatVersion, sizeof(kFileFormatVersion), 1, file) != 1) {
     LOG(ERROR) << "Failed to write file version";
@@ skipping 72 matching lines @@
       return false;
     }
   }
 
   base::CloseFile(file);
 
   return true;
 }
 
 }  // namespace ui