Add headless chrome as an accepted browser string in chromedriver.

chrome/test/chromedriver/chrome/browser_info.cc

Index: chrome/test/chromedriver/chrome/browser_info.cc
diff --git a/chrome/test/chromedriver/chrome/browser_info.cc b/chrome/test/chromedriver/chrome/browser_info.cc
index c790bfd5d6de310e73e5ff24d4d721de4ec0c562..736a6af617d833e0d15d9a065088565c7443f0d5 100644
--- a/chrome/test/chromedriver/chrome/browser_info.cc
+++ b/chrome/test/chromedriver/chrome/browser_info.cc
@@ -19,6 +19,9 @@ namespace {
 const char kVersionPrefix[] = "Chrome/";
 const size_t kVersionPrefixLen = sizeof(kVersionPrefix) - 1;
 
+const char kHeadlessVersionPrefix[] = "HeadlessChrome/";
+const size_t kHeadlessVersionPrefixLen = sizeof(kHeadlessVersionPrefix) - 1;
+
 }  // namespace
 
 BrowserInfo::BrowserInfo()
@@ -104,6 +107,23 @@ Status ParseBrowserString(bool has_android_package,
     }
   }
 
+  if (base::StartsWith(browser_string, kHeadlessVersionPrefix,
+                       base::CompareCase::SENSITIVE)) {
+    std::string version = browser_string.substr(kHeadlessVersionPrefixLen);
+
+    Status status = ParseBrowserVersionString(
+        version, &browser_info->major_version, &build_no);
+    if (status.IsError())
+      return status;
+
+    if (build_no != 0) {
+      browser_info->browser_name = "headless chrome";
+      browser_info->browser_version = version;
+      browser_info->build_no = build_no;
+      return Status(kOk);
+    }
+  }
+
   if (browser_string.find("Version/") == 0u ||   // KitKat
       (has_android_package && build_no == 0)) {  // Lollipop
     size_t pos = browser_string.find(kVersionPrefix);