OS#17588837 - Fast memory growth when serializing many ScopeInfo objects

Change ByteCodeSerializer to serialize unique ScopeInfo objects only once instead of duplicating them in the serialized bytecode. This was causing some websites to allocate quite a bit of memory due to them referencing the same huge ScopeInfo objects many times.

Fixes:
https://microsoft.visualstudio.com/web/wi.aspx?id=17588837

Author: boingoing

lib/Runtime/ByteCode/ByteCodeSerializer.cpp

@@ -100,6 +100,8 @@ namespace Js
         SerializedFuncInfoArray(uint offset, int count);
     };
 
+    typedef uint LocalScopeInfoId;
+
 #pragma pack(pop)
 
     // Holds information about the deserialized bytecode cache. Contains fast inline functions
@@ -111,12 +113,17 @@ namespace Js
         PropertyId * propertyIds;
         int propertyCount;
         int builtInPropertyCount;
+        uint scopeInfoCount;
+        const byte** scopeInfoRelativeOffsets;
 
         typedef JsUtil::BaseDictionary<Js::LocalFunctionId, FunctionInfo*, ArenaAllocator> LocalFunctionIdToFunctionInfoMap;
         LocalFunctionIdToFunctionInfoMap* localFunctionIdToFunctionInfoMap;
+        typedef JsUtil::BaseDictionary<LocalScopeInfoId, ScopeInfo*, ArenaAllocator> LocalScopeInfoIdToScopeInfoMap;
+        LocalScopeInfoIdToScopeInfoMap* localScopeInfoIdToScopeInfoMap;
 
     private:
         LocalFunctionIdToFunctionInfoMap * EnsureLocalFunctionIdToFunctionInfoMap(ScriptContext * scriptContext);
+        LocalScopeInfoIdToScopeInfoMap * EnsureLocalScopeInfoIdToScopeInfoMap(ScriptContext * scriptContext);
 
     public:
         ByteCodeCache(ScriptContext * scriptContext, int builtInPropertyCount);
@@ -127,6 +134,7 @@ namespace Js
 
         void RegisterFunctionIdToFunctionInfo(ScriptContext * scriptContext, LocalFunctionId functionId, FunctionInfo* functionInfo);
         FunctionInfo* LookupFunctionInfo(ScriptContext * scriptContext, LocalFunctionId functionId);
+        ScopeInfo* LookupScopeInfo(ScriptContext * scriptContext, LocalScopeInfoId scopeInfoId);
 
         ByteCodeBufferReader* GetReader()
         {