Increase sharding for slow tests on linux_chromium_asan_rel_ng.

browser_tests has a runtime that varies from 12m to 18m, with
overhead of 1m. By increasing sharding from 30->40, we're keeping overhead below
10%, which reducing runtime by ~5 minutes.

content_browsertests has a runtime of 18 minutes, with overhead of 40s.
Increasing sharding by 2x maintains an overhead of less than 10%, while reducing
runtime by ~9 minutes.

These changes, in addition to sharding improvements to sync_integration_tests
[see https://chromium-review.googlesource.com/c/chromium/src/+/1932475] should
yield a ~15 minute improvement to cycle time of the builder
linux_chromium_asan_rel_ng with minimal impact on fleet capacity.

Bug: 1028289
Change-Id: I11a212f6a349d9bc30c80ec45a22be54fb8f5d2c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1934395
Commit-Queue: Erik Chen <erikchen@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
Auto-Submit: Erik Chen <erikchen@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718871}

testing/buildbot/chromium.memory.json

@@ -3276,7 +3276,7 @@
               "os": "Ubuntu-16.04"
             }
           ],
-          "shards": 30
+          "shards": 40
         },
         "test": "browser_tests"
       },
@@ -3477,7 +3477,7 @@
               "os": "Ubuntu-16.04"
             }
           ],
-          "shards": 6
+          "shards": 12
         },
         "test": "content_browsertests"
       },

testing/buildbot/test_suite_exceptions.pyl

@@ -208,7 +208,7 @@
         # These are very slow on the ASAN trybot for some reason.
         # crbug.com/794372
         'swarming': {
-          'shards': 30,
+          'shards': 40,
         },
       },
       'Mac ASan 64 Tests (1)': {
@@ -484,6 +484,12 @@
           '--disable-features=WebRTC-H264WithOpenH264FFmpeg',
         ],
       },
+      # chromium.memory
+      'Linux ASan LSan Tests (1)': {
+        'swarming': {
+          'shards': 12,
+        },
+      },
       'Linux ASan Tests (sandboxed)': {
         'swarming': {
           'shards': 2, # https://crbug.com/955853