Add command line flags to dump asm.js -> wasm conversion data.

BUG= https://code.google.com/p/v8/issues/detail?id=4203
TEST=manual
R=titzer@chromium.org,aseemgarg@chromium.org
LOG=N

Review URL: https://codereview.chromium.org/1697723002

Cr-Commit-Position: refs/heads/master@{#34009}

src/flag-definitions.h

@@ -482,6 +482,10 @@ DEFINE_BOOL(wasm_break_on_decoder_error, false,
 
 DEFINE_BOOL(enable_simd_asmjs, false, "enable SIMD.js in asm.js stdlib")
 
+DEFINE_BOOL(dump_asmjs_wasm, false, "dump Asm.js to WASM module bytes")
+DEFINE_STRING(asmjs_wasm_dumpfile, "asmjs.wasm",
+              "file to dump asm wasm conversion result to")
+
 DEFINE_INT(typed_array_max_size_in_heap, 64,
            "threshold for in-heap typed array")
 

src/wasm/wasm-js.cc

@@ -126,6 +126,15 @@ v8::internal::wasm::WasmModuleIndex* TranslateAsmModule(
   auto module = v8::internal::wasm::AsmWasmBuilder(
                     info->isolate(), info->zone(), info->literal(), foreign)
                     .Run();
+
+  if (i::FLAG_dump_asmjs_wasm) {
+    FILE* wasm_file = fopen(i::FLAG_asmjs_wasm_dumpfile, "wb");
+    if (wasm_file) {
+      fwrite(module->Begin(), module->End() - module->Begin(), 1, wasm_file);
+      fclose(wasm_file);
+    }
+  }
+
   return module;
 }