When reading the map from a live object, use a barrier load

It could happen that we shrink a live object on the main thread (e.g.
MigrateFastToSlow) while we're sweeping the same page. The main
thread first creates a filler object that the release-stores the new
map. Therefore it's important to barrier load the map word of live
objects from the sweeper thread.

BUG=none
R=ulan@chromium.org,hpayer@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/797623002

Cr-Commit-Position: refs/heads/master@{#25780}
move v8_use_external_startup_data to standalone.gypi

This allows the setting to be overridable by embedders,
at the cost of forcing embedders that don't build v8
using standalone.gypi to add this setting to their build
config.

BUG=chromium:421063
LOG=Y

Review URL: https://codereview.chromium.org/794583002

Cr-Commit-Position: refs/heads/master@{#25781}
Add materialized literals for tagged templates in preparser

LOG=N
R=arv@chromium.org, dslomov@chromium.org, marja@chromium.org
BUG=

Review URL: https://codereview.chromium.org/792083002

Cr-Commit-Position: refs/heads/master@{#25782}
Update tests in preparation for shipping classes.

R=arv@chromium.org
BUG=v8:3330
LOG=N

Review URL: https://codereview.chromium.org/788773003

Cr-Commit-Position: refs/heads/master@{#25783}
Fix builds w/ component=="shared_library" and v8_use_external_startup_data==1.

R=machenbach@chromium.org
BUG=

Review URL: https://codereview.chromium.org/794213002

Cr-Commit-Position: refs/heads/master@{#25784}