Increase shard for browser_tests on win

Currently browser_tests on win7_chromium_rel_ng sometimes took more than 10 mins.
Let me increase the number of shards for such tests.

e.g
753s https://ci.chromium.org/b/8936390613165886176
732s https://ci.chromium.org/b/8936406831776876544
706s https://ci.chromium.org/b/8936396862731996176
704s https://ci.chromium.org/b/8936363432077079248

Bug: 868114
Change-Id: I9a7eb07ce2c58f5b03e5f39152dba7ac6101f11b
Reviewed-on: https://chromium-review.googlesource.com/1203519
Commit-Queue: Takuto Ikuta <[email protected]>
Reviewed-by: John Budorick <[email protected]>
Cr-Commit-Position: refs/heads/master@{#588764}
diff --git a/testing/buildbot/test_suite_exceptions.pyl b/testing/buildbot/test_suite_exceptions.pyl
index b9cbccc..54540a6d 100644
--- a/testing/buildbot/test_suite_exceptions.pyl
+++ b/testing/buildbot/test_suite_exceptions.pyl
@@ -214,6 +214,13 @@
         },
       },
       # chromium.win
+      'Win7 Tests (1)': {
+        # This is for slow test execution that often becomes a critical path of
+        # swarming jobs. crbug.com/868114
+        'swarming': {
+          'shards': 15,
+        },
+      },
       'Win7 Tests (dbg)(1)': {
         'swarming': {
           'shards': 20,