[wasm][asm.js] Turning on asm.js->wasm when ignition_staging is on.

BUG=v8:4203
R=danno@chromium.org,titzer@chromium.org,rmcilroy@chromium.org

Review-Url: https://codereview.chromium.org/2553963003
Cr-Commit-Position: refs/heads/master@{#41515}

src/flag-definitions.h

@@ -506,6 +506,7 @@ DEFINE_BOOL(wasm_loop_assignment_analysis, true,
             "perform loop assignment analysis for WASM")
 
 DEFINE_BOOL(validate_asm, false, "validate asm.js modules before compiling")
+DEFINE_IMPLICATION(ignition_staging, validate_asm)
 
 DEFINE_BOOL(dump_wasm_module, false, "dump WASM module bytes")
 DEFINE_STRING(dump_wasm_module_path, NULL, "directory to dump wasm modules to")