cros_fuzz: Install 'virtual/implicit-system'

'virtual/implicit-system' is a base package needed to ensure
that basic utilities to be able to chroot in target board's
sysroot is available.

BUG=chromium:1013357
TEST=cros_fuzz shell works.

Change-Id: Ib54c394831a8308e2e1eb219cb416752d2265e7b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1854372
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Reviewed-by: Jonathan Metzman <metzman@chromium.org>
Commit-Queue: Manoj Gupta <manojgupta@chromium.org>
Tested-by: Manoj Gupta <manojgupta@chromium.org>
diff --git a/scripts/cros_fuzz.py b/scripts/cros_fuzz.py
index e1b7594..27662c7 100644
--- a/scripts/cros_fuzz.py
+++ b/scripts/cros_fuzz.py
@@ -1109,6 +1109,14 @@
   SetUpSysrootForFuzzing()
   Reproduce(StripFuzzerPrefixes(options.fuzzer), options.testcase)
 
+def InstallBaseDependencies(options):
+  """ Installs the base packages needed to chroot in board sysroot.
+
+  Args:
+    options: The parsed arguments passed to this program.
+  """
+  build_type = getattr(options, 'build_type', None)
+  BuildPackage('virtual/implicit-system', options.board, build_type)
 
 def ParseArgs(argv):
   """Parses program arguments.
@@ -1208,6 +1216,8 @@
 
   SysrootPath.SetPathToSysroot(options.board)
 
+  InstallBaseDependencies(options)
+
   if options.command == 'cleanup':
     ExecuteCleanupCommand()
   elif options.command == 'coverage':