Double shard dbg builds of net_unittests on linux(-chromos) testers.

Bug: 851996
Change-Id: Id1b01007c65fe417dc9f3beac1aac158e5c97bd0
Reviewed-on: https://chromium-review.googlesource.com/1097701Reviewed-by: John Budorick <jbudorick@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#566712}

testing/buildbot/chromium.chromiumos.json

@@ -407,7 +407,8 @@
       },
       {
         "swarming": {
-          "can_use_on_swarming_builders": true
+          "can_use_on_swarming_builders": true,
+          "shards": 2
         },
         "test": "net_unittests"
       },

testing/buildbot/chromium.linux.json

@@ -2015,7 +2015,8 @@
       },
       {
         "swarming": {
-          "can_use_on_swarming_builders": true
+          "can_use_on_swarming_builders": true,
+          "shards": 2
         },
         "test": "net_unittests"
       },
@@ -2619,7 +2620,8 @@
       },
       {
         "swarming": {
-          "can_use_on_swarming_builders": true
+          "can_use_on_swarming_builders": true,
+          "shards": 2
         },
         "test": "net_unittests"
       },

testing/buildbot/test_suite_exceptions.pyl

@@ -1754,6 +1754,22 @@
           'shards': 4,
         }
       },
+      # The suite runs signficantly slower on linux dbg, so increase shards.
+      'Linux Tests (dbg)(1)': {
+        'swarming': {
+          'shards': 2,
+        },
+      },
+      'Linux Tests (dbg)(1)(32)': {
+        'swarming': {
+          'shards': 2,
+        },
+      },
+      'linux-chromeos-dbg': {
+        'swarming': {
+          'shards': 2,
+        },
+      },
     },
   },
   'network_service_browser_tests': {