[fuchsia] Keep amber repo running during blink_web_tests.

Previously the amber repository only ran during initial package
installation.  Since 2020-04-08 it is required during the entire
test run.

Bug: 1033565
Change-Id: If21cfeefaf8de0a4680aedcd31f79ba35d3e9577
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2159372Reviewed-by: Wez <wez@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Stephen Roe <steveroe@google.com>
Cr-Commit-Position: refs/heads/master@{#763425}

third_party/blink/tools/blinkpy/web_tests/port/fuchsia.py

@@ -127,6 +127,7 @@ class _TargetHost(object):
     def __init__(self, build_path, build_ids_path, ports_to_forward,
                  target_device, results_directory):
         try:
+            self._amber_repo = None
             self._target = None
             target_args = {
                 'output_dir': build_path,
@@ -177,6 +178,9 @@ class _TargetHost(object):
         self.symbolizer = symbolizer.RunSymbolizer(
             self._listener.stdout, listener_log, [build_ids_path])
 
+        self._amber_repo = self._target.GetAmberRepo()
+        self._amber_repo.__enter__()
+
         package_path = os.path.join(build_path, CONTENT_SHELL_PACKAGE_PATH)
         self._target.InstallPackage([package_path])
 
@@ -194,6 +198,8 @@ class _TargetHost(object):
             stderr=subprocess.PIPE)
 
     def cleanup(self):
+        if self._amber_repo:
+            self._amber_repo.__exit__(None, None, None)
         if self._target:
             # TODO(sergeyu): Currently __init__() always starts Qemu, so we can
             # just shutdown it. Update this logic when reusing target devices