Reland "Enable Object.observe by default" again

src/flag-definitions.h

Index: src/flag-definitions.h
diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index 5441a1de118f38a6f0ab8b490d3813069317f1b3..ca9c6bbeaf54af77b1f6d43a94f324e84f921403 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -179,8 +179,6 @@ DEFINE_bool(harmony_promises, false, "enable harmony promises")
 DEFINE_bool(harmony_proxies, false, "enable harmony proxies")
 DEFINE_bool(harmony_collections, false,
             "enable harmony collections (sets, maps, and weak maps)")
-DEFINE_bool(harmony_observation, false,
-            "enable harmony object observation (implies harmony collections")
 DEFINE_bool(harmony_generators, false, "enable harmony generators")
 DEFINE_bool(harmony_iteration, false, "enable harmony iteration (for-of)")
 DEFINE_bool(harmony_numeric_literals, false,
@@ -196,7 +194,6 @@ DEFINE_implication(harmony, harmony_symbols)
 DEFINE_implication(harmony, harmony_promises)
 DEFINE_implication(harmony, harmony_proxies)
 DEFINE_implication(harmony, harmony_collections)
-DEFINE_implication(harmony, harmony_observation)
 DEFINE_implication(harmony, harmony_generators)
 DEFINE_implication(harmony, harmony_iteration)
 DEFINE_implication(harmony, harmony_numeric_literals)
@@ -205,7 +202,6 @@ DEFINE_implication(harmony, harmony_arrays)
 DEFINE_implication(harmony, harmony_maths)
 DEFINE_implication(harmony_promises, harmony_collections)
 DEFINE_implication(harmony_modules, harmony_scoping)
-DEFINE_implication(harmony_observation, harmony_collections)
 
 // Flags for experimental implementation features.
 DEFINE_bool(packed_arrays, true, "optimizes arrays that have no holes")