[swarming] Dogfood exparchive feature

The new swarming archiving method requires isolate files to be copied to the build dir.

BUG=chromium:598990
NOTRY=true
TBR=tandrii@chromium.org,tansell@chromium.org,vogelheim@chromium.org

Change-Id: I87633725d9ce715684f761ce0c8d2691642c5389
Reviewed-on: https://chromium-review.googlesource.com/444644Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43266}

infra/mb/mb_config.pyl

@@ -425,7 +425,7 @@
       'gyp', 'release_bot', 'x64', 'asan', 'bb', 'coverage', 'lsan',
       'minimal_symbols', 'swarming'],
     'gyp_release_x64_cfi_symbolized': [
-      'gyp', 'release_bot', 'x64', 'cfi', 'swarming', 'symbolized'],
+      'gyp', 'release_bot', 'x64', 'cfi', 'swarming_exp', 'symbolized'],
     'gyp_release_x64_gcc_coverage': [
       'gyp', 'release_bot', 'x64', 'coverage', 'gcc'],
 
@@ -635,6 +635,11 @@
       'gyp_defines': 'test_isolation_mode=prepare',
     },
 
+    'swarming_exp': {
+      'gn_args': 'v8_test_isolation_mode="check"',
+      'gyp_defines': 'test_isolation_mode=check',
+    },
+
     # TODO(machenbach): Remove the symbolized config after the bots are gone.
     'symbolized': {
       'gn_args': 'v8_no_inline=true',