PlzNavigate: Enforce 'form-action' CSP on the browser-side.

content/common/navigation_params.h

Index: content/common/navigation_params.h
diff --git a/content/common/navigation_params.h b/content/common/navigation_params.h
index 30fd9e7b47b69b67de600951da199cd1305285d7..b0ae9c94d4055da0a499cdb6aee814a9c9ab84a5 100644
--- a/content/common/navigation_params.h
+++ b/content/common/navigation_params.h
@@ -149,6 +149,7 @@ struct CONTENT_EXPORT BeginNavigationParams {
       bool skip_service_worker,
       RequestContextType request_context_type,
       blink::WebMixedContentContextType mixed_content_context_type,
+      bool is_form_submission,
       const base::Optional<url::Origin>& initiator_origin);
   BeginNavigationParams(const BeginNavigationParams& other);
   ~BeginNavigationParams();
@@ -171,6 +172,9 @@ struct CONTENT_EXPORT BeginNavigationParams {
   // The mixed content context type for potential mixed content checks.
   blink::WebMixedContentContextType mixed_content_context_type;
 
+  // Whether or not the navigation has been initiated by a form submission.
+  bool is_form_submission;
+
   // See WebSearchableFormData for a description of these.
   GURL searchable_form_url;
   std::string searchable_form_encoding;