sandwich: Adds command line flag to disable WPR injections

tools/android/loading/device_setup.py

Index: tools/android/loading/device_setup.py
diff --git a/tools/android/loading/device_setup.py b/tools/android/loading/device_setup.py
index 5782b58a1bed6c6c01782ef3ce9ae4626de80cea..bb05ce3d9fcb95fb5e5e0250caf9a0973b74aa55 100644
--- a/tools/android/loading/device_setup.py
+++ b/tools/android/loading/device_setup.py
@@ -115,7 +115,8 @@ def _SetUpDevice(device, package_info):
 
 
 @contextlib.contextmanager
-def WprHost(device, wpr_archive_path, record=False):
+def WprHost(device, wpr_archive_path, record=False,
+            disable_script_injection=False):
   """Launches web page replay host.
 
   Args:
@@ -140,6 +141,11 @@ def WprHost(device, wpr_archive_path, record=False):
   else:
     assert os.path.exists(wpr_archive_path)
 
+  if disable_script_injection:
+    # Remove default WPR injected scripts like deterministic.js which
+    # overrides Math.random.
+    wpr_server_args.extend(['--inject_scripts', ''])
+
   # Deploy certification authority to the device.
   temp_certificate_dir = tempfile.mkdtemp()
   wpr_ca_cert_path = os.path.join(temp_certificate_dir, 'testca.pem')