Add some logging to a flakey browsertest to debug.

chrome/browser/extensions/extension_browsertest.cc

 #include "chrome/browser/extensions/extension_browsertest.h"
 
 #include "base/command_line.h"
 #include "base/file_path.h"
 #include "base/path_service.h"
 #include "chrome/browser/browser.h"
 #include "chrome/browser/extensions/extension_host.h"
 #include "chrome/browser/extensions/extensions_service.h"
 #include "chrome/browser/profile.h"
 #include "chrome/common/chrome_switches.h"
@@ skipping 50 matching lines @@
 
   registrar_.Add(this, NotificationType::EXTENSION_INSTALLED,
                  NotificationService::AllSources());
   service->InstallExtension(path);
   MessageLoop::current()->PostDelayedTask(FROM_HERE, new MessageLoop::QuitTask,
       kTimeoutMs);
   ui_test_utils::RunMessageLoop();
   registrar_.Remove(this, NotificationType::EXTENSION_INSTALLED,
                     NotificationService::AllSources());
   size_t num_after = service->extensions()->size();
-  if (num_after != (num_before + 1))
+  if (num_after != (num_before + 1)) {
+    std::cout << "Num extensions before: " << IntToString(num_before)
+              << "num after: " << IntToString(num_after)
+              << "Installed extensions are:\n";
+    for (size_t i = 0; i < service->extensions()->size(); ++i)
+      std::cout << "  " << service->extensions()->at(i)->id() << "\n";
     return false;
+  }
 
   return WaitForExtensionHostsToLoad();
 }
 
 void ExtensionBrowserTest::UninstallExtension(const std::string& extension_id) {
   ExtensionsService* service = browser()->profile()->GetExtensionsService();
   service->UninstallExtension(extension_id, false);
 }
 
 bool ExtensionBrowserTest::WaitForExtensionHostsToLoad() {
   // Wait for all the extension hosts that exist to finish loading.
   // NOTE: This assumes that the extension host list is not changing while
   // this method is running.
   ExtensionProcessManager* manager =
         browser()->profile()->GetExtensionProcessManager();
   base::Time start_time = base::Time::Now();
   for (ExtensionProcessManager::const_iterator iter = manager->begin();
      iter != manager->end(); ++iter) {
     while (!(*iter)->did_stop_loading()) {
-      if ((base::Time::Now() - start_time).InMilliseconds() > kTimeoutMs)
+      if ((base::Time::Now() - start_time).InMilliseconds() > kTimeoutMs) {
+        std::cout << "Extension host did not load for URL: "
+                  << (*iter)->GetURL().spec();
         return false;
+      }
 
       MessageLoop::current()->PostDelayedTask(FROM_HERE,
           new MessageLoop::QuitTask, 200);
       ui_test_utils::RunMessageLoop();
     }
   }
 
   return true;
 }
 
 void ExtensionBrowserTest::Observe(NotificationType type,
                      const NotificationSource& source,
                      const NotificationDetails& details) {
   switch (type.value) {
     case NotificationType::EXTENSION_INSTALLED:
     case NotificationType::EXTENSIONS_LOADED:
       MessageLoopForUI::current()->Quit();
       break;
     default:
       NOTREACHED();
       break;
   }
 }