Move Object.observe back to shipping temporarily

Turning it off broke both the trace viewer and using the devtools
to connect to an earlier version of Chrome running on another device.

BUG=chromium:552100, chromium:569417, chromium:569647
TBR=rossberg@chromium.org
LOG=y

Review URL: https://codereview.chromium.org/1521993004 .

Cr-Commit-Position: refs/heads/master@{#32850}

src/flag-definitions.h

@@ -200,7 +200,6 @@ DEFINE_IMPLICATION(es_staging, harmony_reflect)
 
 // Features that are still work in progress (behind individual flags).
 #define HARMONY_INPROGRESS(V)                                         \
-  V(harmony_object_observe, "harmony Object.observe")                 \
   V(harmony_modules, "harmony modules")                               \
   V(harmony_proxies, "harmony proxies")                               \
   V(harmony_unicode_regexps, "harmony unicode regexps")               \
@@ -224,6 +223,7 @@ DEFINE_IMPLICATION(es_staging, harmony_reflect)
   V(harmony_default_parameters, "harmony default parameters") \
   V(harmony_destructuring_bind, "harmony destructuring bind") \
   V(harmony_concat_spreadable, "harmony isConcatSpreadable")  \
+  V(harmony_object_observe, "harmony Object.observe")         \
   V(harmony_tolength, "harmony ToLength")                     \
   V(harmony_tostring, "harmony toString")                     \
   V(harmony_completion, "harmony completion value semantics") \