[Fuchsia] Providing FUCHSIA_SDK_PATH env var for fuchsia lsc (#51234)

This change updates test-scripts with https://crrev.com/c/5347216 so that it can override the sdk location from an env var. The override location can be used by update_product_bundles to download emulator images of an unreleased sdk from gcs buckets. The process is used by fuchsia lsc (https://ci.chromium.org/ui/p/turquoise/builders/global.ci/sdk-core-linux-flutter), now it's failing due to the wrong product_bundle location being used.

This change should have no impact to the existing builders since they do not use either gclient variables relevant. E.g. download_fuchsia_sdk and fuchsia_sdk_path.

Bug: http://b/328110079

FYI: @mbrase 

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: zijiehe-google-com

DEPS

@@ -257,7 +257,7 @@ vars = {
   # The version / instance id of the cipd:chromium/fuchsia/test-scripts which
   # will be used altogether with fuchsia-sdk to setup the build / test
   # environment.
-  'fuchsia_test_scripts_version': 'vf8imeAzGv_gjYQDoqub2laI-6nkB3gQNiGuVaFForMC',
+  'fuchsia_test_scripts_version': 'XtkBHdNTtIpWdxN_lUNf6VqnvPUhvGTYgPDqob1R65EC',
 
   # The version / instance id of the cipd:chromium/fuchsia/gn-sdk which will be
   # used altogether with fuchsia-sdk to generate gn based build rules.
@@ -1205,6 +1205,9 @@ hooks = [
     'pattern': '.',
     'condition': 'run_fuchsia_emu',
     'action': [
+      'env',
+      'DOWNLOAD_FUCHSIA_SDK={download_fuchsia_sdk}',
+      'FUCHSIA_SDK_PATH={fuchsia_sdk_path}',
       'python3',
       'src/flutter/tools/fuchsia/with_envs.py',
       'src/flutter/tools/fuchsia/test_scripts/update_product_bundles.py',

tools/fuchsia/with_envs.py

@@ -30,6 +30,13 @@ def Main():
   assert platform.system() == 'Linux', 'Unsupported OS ' + platform.system()
   os.environ['FUCHSIA_SDK_ROOT'] = os.path.join(os.environ['SRC_ROOT'], 'fuchsia/sdk/linux/')
 
+  if os.getenv('DOWNLOAD_FUCHSIA_SDK') == 'True':
+    sdk_path = os.environ['FUCHSIA_SDK_PATH']
+    assert sdk_path.endswith('/linux-amd64/core.tar.gz')
+    assert not sdk_path.startswith('/')
+    os.environ['FUCHSIA_SDK_OVERRIDE'
+              ] = 'gs://fuchsia-artifacts/' + sdk_path[:-len('/linux-amd64/core.tar.gz')]
+
   with subprocess.Popen(sys.argv[1:]) as proc:
     try:
       proc.wait()