headless: Add a small C++ example application

headless/app/headless_shell.cc

Index: headless/app/headless_shell.cc
diff --git a/headless/app/headless_shell.cc b/headless/app/headless_shell.cc
index 942fb9bbad7084131d5f94af51c8bdb28cc6e313..47e68e76d21dff0264a5866e4170399ef4d00749 100644
--- a/headless/app/headless_shell.cc
+++ b/headless/app/headless_shell.cc
@@ -56,9 +56,9 @@ bool ParseWindowSize(std::string window_size, gfx::Size* parsed_window_size) {
 
 // An application which implements a simple headless browser.
 class HeadlessShell : public HeadlessWebContents::Observer,
-                      emulation::ExperimentalObserver,
-                      inspector::ExperimentalObserver,
-                      page::Observer {
+                      public emulation::ExperimentalObserver,
+                      public inspector::ExperimentalObserver,
+                      public page::Observer {
  public:
   HeadlessShell()
       : browser_(nullptr),
@@ -257,13 +257,13 @@ class HeadlessShell : public HeadlessWebContents::Observer,
 
   void FetchDom() {
     devtools_client_->GetRuntime()->Evaluate(
-        "document.body.innerHTML",
+        "document.body.outerHTML",
         base::Bind(&HeadlessShell::OnDomFetched, weak_factory_.GetWeakPtr()));
   }
 
   void OnDomFetched(std::unique_ptr<runtime::EvaluateResult> result) {
     if (result->HasExceptionDetails()) {
-      LOG(ERROR) << "Failed to evaluate document.body.innerHTML: "
+      LOG(ERROR) << "Failed to evaluate document.body.outerHTML: "
                  << result->GetExceptionDetails()->GetText();
     } else {
       std::string dom;