headless: Enable GL support by default

headless/public/headless_browser.h

Index: headless/public/headless_browser.h
diff --git a/headless/public/headless_browser.h b/headless/public/headless_browser.h
index b98a40acd866820ba10df3fff87d1adaf9ec95f7..e0c91fa05e4c304652a68662a1cf83854268d716 100644
--- a/headless/public/headless_browser.h
+++ b/headless/public/headless_browser.h
@@ -117,6 +117,11 @@ struct HeadlessBrowser::Options {
   // fetching for different network schemes.
   ProtocolHandlerMap protocol_handlers;
 
+  // Choose the GL implementation to use for rendering. A suitable
+  // implementantion is selected by default. Setting this to an empty
+  // string can be used to disable GL rendering (e.g., WebGL support).
+  std::string gl_implementation;
+
  private:
   Options(int argc, const char** argv);
 
@@ -136,6 +141,7 @@ class HeadlessBrowser::Options::Builder {
   Builder& SetHostResolverRules(const std::string& host_resolver_rules);
   Builder& SetSingleProcessMode(bool single_process_mode);
   Builder& SetProtocolHandlers(ProtocolHandlerMap protocol_handlers);
+  Builder& SetGLImplementation(const std::string& gl_implementation);
 
   Options Build();