Reland "Add tests to Fuchsia ARM64 CI builder."

This is a reland of 4486011f

crrev.com/c/2068517 fixes the test isolate issue in crbug.com/1054837 which required the revert.

Original change's description:
> Add tests to Fuchsia ARM64 CI builder.
>
> Use the same test exceptions for Fuchsia ARM64 as fuchsia-fyi-arm64-rel.
>
> Bug: 1042512
> Change-Id: I7b9333e49151975b4bfecb98dd6d36d954b514ef
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2067673
> Reviewed-by: John Budorick <jbudorick@chromium.org>
> Commit-Queue: Stephen Roe <steveroe@google.com>
> Cr-Commit-Position: refs/heads/master@{#743555}

Bug: 1042512
Change-Id: If2cbb6cdc5ddecdd0e3454ef22cfe28f4978b4bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2066665Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Stephen Roe <steveroe@google.com>
Cr-Commit-Position: refs/heads/master@{#743723}

testing/buildbot/test_suite_exceptions.pyl

@@ -364,6 +364,7 @@
   'components_unittests': {
     'remove_from': [
       'Fuchsia x64', # https://crbug.com/961457
+      'Fuchsia ARM64', # https://crbug.com/961457
       'android-code-coverage-native', # crbug/1018431
       'fuchsia-fyi-arm64-rel',  # https://crbug.com/961457
       'fuchsia-fyi-x64-dbg',  # https://crbug.com/961457
@@ -1038,6 +1039,7 @@
   'net_unittests': {
     'remove_from': [
       'chromeos-amd64-generic-rel',  # https://crbug.com/1053547
+      'Fuchsia ARM64',  # https://crbug.com/877248
       'fuchsia-fyi-arm64-rel',  # https://crbug.com/877248
       'fuchsia-fyi-x64-dbg',  # https://crbug.com/844416
     ],

testing/buildbot/waterfalls.pyl

@@ -3585,6 +3585,14 @@
         'additional_compile_targets': [
           'all',
         ],
+        'test_suites': {
+          'gtest_tests': 'fuchsia_gtests',
+        },
+        'mixins': [
+          'arm64',
+          'docker',
+          'linux-xenial',
+        ],
       },
       'Fuchsia x64': {
         'additional_compile_targets': [