snapshot: Add a minimal ModuleSnapshotMinidump and accessor from ProcessSnapshotMinidump

snapshot/minidump/minidump_simple_string_dictionary_reader.cc

Index: snapshot/minidump/minidump_simple_string_dictionary_reader.cc
diff --git a/snapshot/minidump/minidump_simple_string_dictionary_reader.cc b/snapshot/minidump/minidump_simple_string_dictionary_reader.cc
index 685266d74d5450da9eddcacad8263ca1ca8a154f..88399452be5fbc0f8f57d08b0a9231b088e0e77e 100644
--- a/snapshot/minidump/minidump_simple_string_dictionary_reader.cc
+++ b/snapshot/minidump/minidump_simple_string_dictionary_reader.cc
@@ -28,8 +28,9 @@ bool ReadMinidumpSimpleStringDictionary(
     FileReaderInterface* file_reader,
     const MINIDUMP_LOCATION_DESCRIPTOR& location,
     std::map<std::string, std::string>* dictionary) {
+  dictionary->clear();
+
   if (location.Rva == 0) {
-    dictionary->clear();
     return true;
   }
 
@@ -48,7 +49,8 @@ bool ReadMinidumpSimpleStringDictionary(
   }
 
   if (location.DataSize !=
-      entry_count * sizeof(MinidumpSimpleStringDictionaryEntry)) {
+      sizeof(MinidumpSimpleStringDictionary) +
+          entry_count * sizeof(MinidumpSimpleStringDictionaryEntry)) {
     LOG(ERROR) << "simple_string_dictionary size mismatch";
     return false;
   }
@@ -73,15 +75,14 @@ bool ReadMinidumpSimpleStringDictionary(
       continue;
     }
 
-    if (local_dictionary.find(key) != local_dictionary.end()) {
+    if (dictionary->find(key) != dictionary->end()) {
       LOG(WARNING) << "duplicate key " << key << ", discarding value " << value;
       continue;
     }
 
-    local_dictionary.insert(std::make_pair(key, value));
+    dictionary->insert(std::make_pair(key, value));
   }
 
-  dictionary->swap(local_dictionary);
   return true;
 }