Re-enable Web Components v0 for Headless clients

See crbug.com/1049126 - the origin trial system is not supported
by headless clients. See [1] which does not override the implementation
of GetOriginTrialPolicy(). In the meantime, we need to re-enable Web
Components v0 for all headless clients to avoid site breakage.

[1] https://source.chromium.org/chromium/chromium/src/+/master:headless/lib/headless_content_client.h
[2] https://source.chromium.org/chromium/chromium/src/+/master:content/public/common/content_client.cc;l=104;drc=2271977bc199216d8266c8a99f8a0b4f147ae0cc

Bug: 1049126
Change-Id: I9af33d03ad34d4ed23a8f5680641ff2066a02840
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2039601
Auto-Submit: Mason Freed <masonfreed@chromium.org>
Reviewed-by: Jason Chase <chasej@chromium.org>
Reviewed-by: Johannes Henkel <johannes@chromium.org>
Commit-Queue: Mason Freed <masonfreed@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738720}

headless/lib/renderer/headless_content_renderer_client.cc

@@ -19,6 +19,12 @@ HeadlessContentRendererClient::HeadlessContentRendererClient() = default;
 
 HeadlessContentRendererClient::~HeadlessContentRendererClient() = default;
 
+bool HeadlessContentRendererClient::RequiresWebComponentsV0(const GURL& url) {
+  // TODO(1049126): Headless clients do not (yet) support origin trials.
+  // In the meantime, re-enable Web Components v0 on all headless clients.
+  return true;
+}
+
 void HeadlessContentRendererClient::RenderFrameCreated(
     content::RenderFrame* render_frame) {
 #if BUILDFLAG(ENABLE_PRINTING)

headless/lib/renderer/headless_content_renderer_client.h

@@ -14,6 +14,8 @@ class HeadlessContentRendererClient : public content::ContentRendererClient {
   HeadlessContentRendererClient();
   ~HeadlessContentRendererClient() override;
 
+  bool RequiresWebComponentsV0(const GURL& url) override;
+
  private:
   void RenderFrameCreated(content::RenderFrame* render_frame) override;