[wasm] Add --trace-wasm-ast-start and --trace-wasm-ast-end options and improve tracing.

src/compiler/wasm-compiler.cc

Index: src/compiler/wasm-compiler.cc
diff --git a/src/compiler/wasm-compiler.cc b/src/compiler/wasm-compiler.cc
index 245d921b9da6fef6aa1eab16fa345c0777fa4aa3..c4bde203fa71de431a8f4c0d7382348b3928504e 100644
--- a/src/compiler/wasm-compiler.cc
+++ b/src/compiler/wasm-compiler.cc
@@ -2594,6 +2594,11 @@ Handle<Code> CompileWasmFunction(wasm::ErrorThrower& thrower, Isolate* isolate,
     return Handle<Code>::null();
   }
 
+  int index = static_cast<int>(function.func_index);
+  if (index >= FLAG_trace_wasm_ast_start && index < FLAG_trace_wasm_ast_end) {
+    PrintAst(body);
+  }
+
   if (FLAG_trace_wasm_decode_time) {
     decode_ms = decode_timer.Elapsed().InMillisecondsF();
   }