[wasm] Initial commit for the Int64Reducer.

src/compiler/wasm-compiler.h

Index: src/compiler/wasm-compiler.h
diff --git a/src/compiler/wasm-compiler.h b/src/compiler/wasm-compiler.h
index 6742d06a75a0383eaea36c880f5c320dd057e9f7..3fd52aa57753fb7c3679eaef8862a04274ad6616 100644
--- a/src/compiler/wasm-compiler.h
+++ b/src/compiler/wasm-compiler.h
@@ -132,6 +132,8 @@ class WasmGraphBuilder {
 
   wasm::FunctionSig* GetFunctionSignature() { return function_signature_; }
 
+  void Int64LoweringForTesting();
+
  private:
   static const int kDefaultBufferSize = 16;
   friend class WasmTrapHelper;