[turbofan] Enable sharing of context-independent code.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/1215643002

Cr-Commit-Position: refs/heads/master@{#29321}

src/flag-definitions.h

@@ -430,7 +430,7 @@ DEFINE_BOOL(turbo_stress_loop_peeling, false,
             "stress loop peeling optimization")
 DEFINE_BOOL(turbo_cf_optimization, true, "optimize control flow in TurboFan")
 DEFINE_BOOL(turbo_frame_elision, true, "elide frames in TurboFan")
-DEFINE_BOOL(turbo_cache_shared_code, false, "cache context-independent code")
+DEFINE_BOOL(turbo_cache_shared_code, true, "cache context-independent code")
 
 DEFINE_INT(typed_array_max_size_in_heap, 64,
            "threshold for in-heap typed array")