[ChromeDriver] Use Browser.close to quit

Currently, ChromeDriver closes desktop Chrome by simply killing the
top-level Chrome process. This isn't graceful, and causes problems
in some scenarios. This commit sends a Browser.close command to close
the browser gracefully.

Bug: chromedriver:2311
Change-Id: Idec9338b094f0aab89022b8453dd2a98268ad1e7
Reviewed-on: https://chromium-review.googlesource.com/1037585
Commit-Queue: John Chen <johnchen@chromium.org>
Reviewed-by: Jonathon Kereliuk <kereliuk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556689}

chrome/test/chromedriver/chrome/chrome_desktop_impl.cc

@@ -207,6 +207,15 @@ bool ChromeDesktopImpl::IsNetworkConnectionEnabled() const {
 }
 
 Status ChromeDesktopImpl::QuitImpl() {
+  Status status = devtools_websocket_client_->ConnectIfNecessary();
+  if (status.IsOk()) {
+    status = devtools_websocket_client_->SendCommandAndIgnoreResponse(
+        "Browser.close", base::DictionaryValue());
+    if (status.IsOk() && process_.WaitForExitWithTimeout(
+                             base::TimeDelta::FromSeconds(10), nullptr))
+      return status;
+  }
+
   // If the Chrome session uses a custom user data directory, try sending a
   // SIGTERM signal before SIGKILL, so that Chrome has a chance to write
   // everything back out to the user data directory and exit cleanly. If we're