[headless] Add default browser context to HeadlessBrowser.

headless/lib/browser/headless_browser_impl.cc

Index: headless/lib/browser/headless_browser_impl.cc
diff --git a/headless/lib/browser/headless_browser_impl.cc b/headless/lib/browser/headless_browser_impl.cc
index 876be95cdc802db462bc1876df03d2d11e8597b5..93d6918a76c8d022a1f46f57296f2c8f5da45f1a 100644
--- a/headless/lib/browser/headless_browser_impl.cc
+++ b/headless/lib/browser/headless_browser_impl.cc
@@ -54,6 +54,7 @@ HeadlessBrowserImpl::HeadlessBrowserImpl(
     : on_start_callback_(on_start_callback),
       options_(std::move(options)),
       browser_main_parts_(nullptr),
+      default_browser_context_(nullptr),
       weak_ptr_factory_(this) {}
 
 HeadlessBrowserImpl::~HeadlessBrowserImpl() {}
@@ -158,6 +159,19 @@ void HeadlessBrowserImpl::DestroyBrowserContext(
   auto it = browser_contexts_.find(browser_context->Id());
   DCHECK(it != browser_contexts_.end());
   browser_contexts_.erase(it);
+  if (default_browser_context_ == browser_context)
+    SetDefaultBrowserContext(nullptr);
+}
+
+void HeadlessBrowserImpl::SetDefaultBrowserContext(
+    HeadlessBrowserContext* browser_context) {
+  DCHECK(!browser_context ||
+         this == HeadlessBrowserContextImpl::From(browser_context)->browser());
+  default_browser_context_ = browser_context;
+}
+
+HeadlessBrowserContext* HeadlessBrowserImpl::GetDefaultBrowserContext() {
+  return default_browser_context_;
 }
 
 base::WeakPtr<HeadlessBrowserImpl> HeadlessBrowserImpl::GetWeakPtr() {