Increase the sharding parallelism for browser_tests on Mac and Windows.

With the NG trybots using the buildbot value, browser_tests' sharding value regressed from the original 8 to 5 shards. The bots are now seeing more delays. Bump everything up to 10.

R=maruel@chromium.org

Review URL: https://codereview.chromium.org/805913004

Cr-Commit-Position: refs/heads/master@{#308408}

testing/buildbot/chromium.mac.json

@@ -23,7 +23,7 @@
         "test": "browser_tests",
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "shards": 5
+          "shards": 10
         }
       },
       "cacheinvalidation_unittests",
@@ -146,7 +146,7 @@
         "test": "browser_tests",
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "shards": 5
+          "shards": 10
         }
       },
       "cacheinvalidation_unittests",

testing/buildbot/chromium.win.json

@@ -15,7 +15,7 @@
         "test": "browser_tests",
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "shards": 7
+          "shards": 10
         }
       },
       "cacheinvalidation_unittests",
@@ -119,7 +119,7 @@
         "test": "browser_tests",
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "shards": 7
+          "shards": 10
         }
       },
       "cacheinvalidation_unittests",
@@ -233,7 +233,7 @@
         "test": "browser_tests",
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "shards": 7
+          "shards": 10
         }
       },
       "cacheinvalidation_unittests",
@@ -344,7 +344,7 @@
         "test": "browser_tests",
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "shards": 6
+          "shards": 10
         }
       },
       "app_installer_unittests",