Implement basic array prefetching hints in Hydrogen.

src/flag-definitions.h

Index: src/flag-definitions.h
===================================================================
--- src/flag-definitions.h	(revision 13350)
+++ src/flag-definitions.h	(working copy)
@@ -181,6 +181,7 @@
 DEFINE_int(max_inlined_nodes_cumulative, 196,
            "maximum cumulative number of AST nodes considered for inlining")
 DEFINE_bool(loop_invariant_code_motion, true, "loop invariant code motion")
+DEFINE_bool(array_prefetch_hint, true, "insert array prefetching hints")
 DEFINE_bool(fast_math, true, "faster (but maybe less accurate) math functions")
 DEFINE_bool(collect_megamorphic_maps_from_stub_cache,
             true,
@@ -193,6 +194,7 @@
 DEFINE_bool(trace_all_uses, false, "trace all use positions")
 DEFINE_bool(trace_range, false, "trace range analysis")
 DEFINE_bool(trace_gvn, false, "trace global value numbering")
+DEFINE_bool(trace_prefetch_hint, false, "trace array prefetch hint")
 DEFINE_bool(trace_representation, false, "trace representation types")
 DEFINE_bool(stress_pointer_maps, false, "pointer map for every instruction")
 DEFINE_bool(stress_environments, false, "environment for every instruction")