[infra] Shard dart2js unit tests

Fixes: b/200928253
Change-Id: I12ec3a5cf714b3b0427d3698dcaf02fef7fe15cc
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/214403
Reviewed-by: William Hesse <whesse@google.com>
Reviewed-by: Sigmund Cherem <sigmund@google.com>
Commit-Queue: Alexander Thomas <athom@google.com>

tools/bots/test_matrix.json

@@ -412,6 +412,17 @@
         "use-sdk": true
       }
     },
+    "web-unittest-asserts-(linux|mac|win)": {
+      "options": {
+        "builder-tag": "web",
+        "compiler": "dartk",
+        "enable-asserts": true,
+        "mode": "release",
+        "runtime": "vm",
+        "timeout": 240,
+        "use-sdk": true
+      }
+    },
     "unittest-asserts-(debug|product|release)-(linux|mac|win)": {
       "options": {
         "compiler": "dartk",
@@ -421,15 +432,6 @@
         "use-sdk": true
       }
     },
-    "unittest-weak-asserts-no-sdk-(linux|mac|win)": {
-      "options": {
-        "compiler": "dartk",
-        "enable-asserts": true,
-        "mode": "release",
-        "runtime": "vm",
-        "timeout": 240
-      }
-    },
     "analyzer-unittest-asserts-(debug|product|release)-(linux|mac|win)": {
       "options": {
         "compiler": "dartk",
@@ -456,15 +458,6 @@
     "vm-ffi-unit-test": {
       "__comment__": "This configuration is only used for a custom test runner. If it conflicts with a new configuration you are adding, you can make this configuration more specific by adding options."
     },
-    "unittest-asserts-no-sdk-(linux|mac|win)": {
-      "options": {
-        "compiler": "dartk",
-        "enable-asserts": true,
-        "mode": "release",
-        "runtime": "vm",
-        "timeout": 240
-      }
-    },
     "unittest-analyzer_use_fasta-(linux|mac|win)": {
       "options": {
         "compiler": "none",
@@ -2457,7 +2450,7 @@
           "testRunner": true,
           "arguments": [
             "pkg/compiler/tool/modular_test_suite.dart",
-            "-nunittest-asserts-no-sdk-linux",
+            "-nweb-unittest-asserts-linux",
             "--verbose",
             "--use-sdk"
           ]
@@ -2465,16 +2458,18 @@
         {
           "name": "js_runtime unit tests",
           "arguments": [
-            "-nunittest-asserts-no-sdk-linux",
+            "-nweb-unittest-asserts-linux",
             "pkg//js_runtime/"
           ]
         },
         {
           "name": "dart2js unit tests",
           "arguments": [
-            "-nunittest-asserts-no-sdk-linux",
+            "-nweb-unittest-asserts-linux",
             "pkg//compiler/"
-          ]
+          ],
+          "shards": 3,
+          "fileset": "web_platform"
         }
       ]
     },