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

ui/base/resource/data_pack.cc

Index: ui/base/resource/data_pack.cc
diff --git a/ui/base/resource/data_pack.cc b/ui/base/resource/data_pack.cc
index f9fe9b8469eeb35d3369a4c32cb09ace5ba48b0f..b3891c2968de9fad66a27f135a9a89f0b83e39ac 100644
--- a/ui/base/resource/data_pack.cc
+++ b/ui/base/resource/data_pack.cc
@@ -231,6 +231,23 @@ 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(GetScaleForScaleFactor(handle->GetScaleFactor()) !=
+                 resource_scale ||
+             !handle->HasResource(resource_id));

[Nico, 2015/05/06 01:06:35]

(nit: if you want I think you can use dcheck_implies for this)

[sadrul, 2015/05/06 17:29:24]

Done.

+    }
+  }
+}
+#endif  // DCHECK_IS_ON()
+
 // static
 bool DataPack::WritePack(const base::FilePath& path,
                          const std::map<uint16, base::StringPiece>& resources,