Test runner: make inspector tests reuse a single inspector process.

content/shell/browser/layout_test/layout_test_devtools_frontend.h

Index: content/shell/browser/layout_test/layout_test_devtools_frontend.h
diff --git a/content/shell/browser/layout_test/layout_test_devtools_frontend.h b/content/shell/browser/layout_test/layout_test_devtools_frontend.h
index 5106a9beca7bbd5bbe750c4ee557db0c5e13e2cb..20db64437b8effb7953d86c9c455ee3c25b2d035 100644
--- a/content/shell/browser/layout_test/layout_test_devtools_frontend.h
+++ b/content/shell/browser/layout_test/layout_test_devtools_frontend.h
@@ -24,11 +24,18 @@ class LayoutTestDevToolsFrontend : public ShellDevToolsFrontend {
   static GURL GetDevToolsPathAsURL(const std::string& settings,
                                    const std::string& frontend_url);
 
+  void ReuseFrontend(WebContents* inspected_contents,
+                     const std::string& settings,
+                     const std::string frontend_url);
+
  private:
   LayoutTestDevToolsFrontend(Shell* frontend_shell,
                              DevToolsAgentHost* agent_host);
   ~LayoutTestDevToolsFrontend() override;
 
+  // content::DevToolsAgentHostClient implementation.
+  void AgentHostClosed(DevToolsAgentHost* agent_host, bool replaced) override;
+
   // WebContentsObserver implementation.
   void RenderProcessGone(base::TerminationStatus status) override;