headless: Implement screenshot capturing

headless/lib/headless_devtools_client_browsertest.cc

Index: headless/lib/headless_devtools_client_browsertest.cc
diff --git a/headless/lib/headless_devtools_client_browsertest.cc b/headless/lib/headless_devtools_client_browsertest.cc
index 5e073a8f31e0b8bdfef7af6ea237df74de9921d0..30e9b811eb914fadc7af12f7edf711b8368e0f30 100644
--- a/headless/lib/headless_devtools_client_browsertest.cc
+++ b/headless/lib/headless_devtools_client_browsertest.cc
@@ -24,6 +24,8 @@ namespace headless {
   class AsyncHeadlessBrowserTestNeedsSemicolon##TEST_FIXTURE_NAME {}
 
 // A test fixture which attaches a devtools client before starting the test.
+// TODO(eseckler): Use the reusable HeadlessAsyncDevTooledTest and macro from
+// headless_browser_test.h instead of this class.
 class HeadlessDevToolsClientTest : public HeadlessBrowserTest,
                                    public HeadlessWebContents::Observer {
  public: