[MERGE #5212 @boingoing] OS#17588837 - Fast memory growth when serializing many ScopeInfo objects

Merge pull request #5212 from boingoing:memleak_scopeinfo_master

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()
         {