OOR-CORS: Add an experimental Feature to enforce extraHeaders option

We are planning to provide a temporary policy escape hatch for
the OOR-CORS enterprise-friendly rollout. With this policy, Chrome
handles any webRequest API users as specifying "extraHeaders" option
so that such Extension can work without any fix for a while.

Before adding such enterprise policy, we want to run a field trial
if such approach does not introduce any other problems.

This patch adds this escape hatch as a base::Feature trial. We will
run a field trials in non-stable channels for a while, and convert this
to an enterprise policy for m79.

Bug: 1000982
Change-Id: I27b96d4fbc70fb52eb2c878058d0fd22078fd339
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1792506Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Commit-Queue: Takashi Toyoshima <toyoshim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695549}

extensions/browser/api/web_request/web_request_api_helpers.cc

@@ -37,6 +37,7 @@
 #include "extensions/browser/extension_system.h"
 #include "extensions/browser/extensions_browser_client.h"
 #include "extensions/browser/runtime_data.h"
+#include "extensions/common/extension_features.h"
 #include "extensions/common/extension_messages.h"
 #include "net/cookies/cookie_util.h"
 #include "net/cookies/parsed_cookie.h"
@@ -334,7 +335,10 @@ IgnoredAction::IgnoredAction(IgnoredAction&& rhs) = default;
 
 bool ExtraInfoSpec::InitFromValue(const base::ListValue& value,
                                   int* extra_info_spec) {
-  *extra_info_spec = 0;
+  *extra_info_spec = base::FeatureList::IsEnabled(
+                         extensions_features::kForceWebRequestExtraHeaders)
+                         ? EXTRA_HEADERS
+                         : 0;
   for (size_t i = 0; i < value.GetSize(); ++i) {
     std::string str;
     if (!value.GetString(i, &str))

extensions/common/extension_features.cc

@@ -6,6 +6,12 @@
 
 namespace extensions_features {
 
+// Forces to handle event listeners as it specifies the "extraHeaders" option.
+// TODO(crbug.com/1000982, 1000984): Run a field trial, and convert to a
+// short-term enterprise policy.
+const base::Feature kForceWebRequestExtraHeaders{
+    "ForceWebRequestExtraHeaders", base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Forces requests to go through WebRequestProxyingURLLoaderFactory.
 const base::Feature kForceWebRequestProxyForTest{
     "ForceWebRequestProxyForTest", base::FEATURE_DISABLED_BY_DEFAULT};

extensions/common/extension_features.h

@@ -9,6 +9,7 @@
 
 namespace extensions_features {
 
+extern const base::Feature kForceWebRequestExtraHeaders;
 extern const base::Feature kForceWebRequestProxyForTest;
 
 }  // namespace extensions_features