[serializer] print use count of external references.

src/snapshot/serializer-common.cc

Index: src/snapshot/serializer-common.cc
diff --git a/src/snapshot/serializer-common.cc b/src/snapshot/serializer-common.cc
index d42c3061e6f5fd3596617161a81e64bb0b372a91..f18879341931465f456bf36095ac0d84262d0375 100644
--- a/src/snapshot/serializer-common.cc
+++ b/src/snapshot/serializer-common.cc
@@ -8,25 +8,21 @@
 #include "src/ic/stub-cache.h"
 #include "src/list-inl.h"
 
-#if defined(DEBUG) && defined(V8_OS_LINUX) && !defined(V8_OS_ANDROID)
-#define SYMBOLIZE_FUNCTION
-#include <execinfo.h>
-#endif  // DEBUG && V8_OS_LINUX && !V8_OS_ANDROID
-
 namespace v8 {
 namespace internal {
 
 ExternalReferenceEncoder::ExternalReferenceEncoder(Isolate* isolate) {
   map_ = isolate->external_reference_map();
+#ifdef DEBUG
+  table_ = ExternalReferenceTable::instance(isolate);
+#endif  // DEBUG
   if (map_ != nullptr) return;
   map_ = new AddressToIndexHashMap();
   ExternalReferenceTable* table = ExternalReferenceTable::instance(isolate);
   for (uint32_t i = 0; i < table->size(); ++i) {
     Address addr = table->address(i);
-    // We expect no duplicate external references entries in the table.
-    // AccessorRefTable getter may have duplicates, indicated by an empty string
-    // as name.
-    DCHECK(table->name(i)[0] == '\0' || map_->Get(addr).IsNothing());
+    DCHECK(map_->Get(addr).IsNothing() ||
+           strncmp(table->name(i), "Redirect to ", 12) == 0);
     map_->Set(addr, i);
     DCHECK(map_->Get(addr).IsJust());
   }
@@ -36,13 +32,14 @@ ExternalReferenceEncoder::ExternalReferenceEncoder(Isolate* isolate) {
 uint32_t ExternalReferenceEncoder::Encode(Address address) const {
   Maybe<uint32_t> maybe_index = map_->Get(address);
   if (maybe_index.IsNothing()) {
-    void* function_addr = address;
-    v8::base::OS::PrintError("Unknown external reference %p.\n", function_addr);
-#ifdef SYMBOLIZE_FUNCTION
-    v8::base::OS::PrintError("%s\n", backtrace_symbols(&function_addr, 1)[0]);
-#endif  // SYMBOLIZE_FUNCTION
+    void* addr = address;
+    v8::base::OS::PrintError("Unknown external reference %p.\n", addr);
+    v8::base::OS::PrintError("%s", ExternalReferenceTable::ResolveSymbol(addr));
     v8::base::OS::Abort();
   }
+#ifdef DEBUG
+  table_->increment_count(maybe_index.FromJust());
+#endif  // DEBUG
   return maybe_index.FromJust();
 }