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..ad3bcfec030c5a0882c597378de4eb09f1441ad0 100644
--- a/ui/base/resource/data_pack.cc
+++ b/ui/base/resource/data_pack.cc
@@ -6,6 +6,8 @@
 
 #include <errno.h>
 
+#include <algorithm>
+
 #include "base/files/file_util.h"
 #include "base/files/memory_mapped_file.h"
 #include "base/logging.h"
@@ -231,6 +233,24 @@ 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) {

[Nico, 2015/05/02 00:50:48]

why + 1?

[sadrul, 2015/05/02 04:17:09]

I am following the code from DataPack::LoadImpl() above (lines 157+). I
considered introducing a
DataPack::ForEachDataPackEntry(void(*func)(DataPackEntry*)), and use that from
both places, since this looks a bit subtle, but decided against it. WDYT?

+    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_);
+    std::for_each(packs.begin(), packs.end(),
+                  [resource_id, resource_scale](const ResourceHandle* handle) {
+                    DCHECK(GetScaleForScaleFactor(handle->GetScaleFactor()) !=
+                               resource_scale ||
+                           !handle->HasResource(resource_id));
+                  });

[Nico, 2015/05/02 00:50:48]

nit: Writing this as

    for (const ResourceHandle* handle : packs) {
      DCHECK(GetScaleForScaleFactor(handle->GetScaleFactor()) !=
                 resource_scale ||
             !handle->HasResource(resource_id));
    }

is both shorter and more readable

[sadrul, 2015/05/02 04:17:09]

Heh, yeah. Totally. Done.

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