[wasm] Enable --wasm-shared-code by default.

R=titzer@chromium.org
BUG=v8:7424

Change-Id: Ic0b8088402a4f64d1a285298a16285bdca4a7167
Reviewed-on: https://chromium-review.googlesource.com/1180897Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55210}

src/flag-definitions.h

@@ -621,7 +621,7 @@ DEFINE_BOOL(wasm_no_stack_checks, false,
 DEFINE_BOOL(wasm_shared_engine, true,
             "shares one wasm engine between all isolates within a process")
 DEFINE_IMPLICATION(future, wasm_shared_engine)
-DEFINE_BOOL(wasm_shared_code, false,
+DEFINE_BOOL(wasm_shared_code, true,
             "shares code underlying a wasm module when it is transferred")
 DEFINE_IMPLICATION(future, wasm_shared_code)
 DEFINE_BOOL(wasm_trap_handler, true,