Add microdump_stackwalk target to chromium.android builders.

testing/buildbot/chromium.android.json

 {
   "Android Cronet Builder": {
     "additional_compile_targets": [
       "cronet_package"
     ]
   },
   "Android N5X Swarm Builder": {
     "gtest_tests": [
       {
         "override_compile_targets": [
@@ skipping 1187 matching lines @@
               "device_os": "MMB29Q",
               "device_type": "bullhead"
             }
           ],
           "hard_timeout": 1200,
           "shards": 1
         }
       }
     ]
   },
+  "Android arm Builder (dbg)": {
+    "additional_compile_targets": [
+      "microdump_stackwalk"
+    ]
+  },
+  "Android arm64 Builder (dbg)": {
+    "additional_compile_targets": [
+      "microdump_stackwalk"
+    ]
+  },
   "KitKat Tablet Tester": {
     "gtest_tests": [
       {
         "test": "android_webview_unittests"
       },
       {
         "test": "base_unittests"
       },
       {
         "override_compile_targets": [
@@ skipping 2356 matching lines @@
       },
       {
         "test": "chrome_sync_shell_test_apk"
       },
       {
         "test": "content_shell_test_apk"
       }
     ]
   }
 }