[ChromeDriver] Support mobile emulation on desktop Chrome.

chrome/test/chromedriver/chrome/stub_chrome.cc

Index: chrome/test/chromedriver/chrome/stub_chrome.cc
diff --git a/chrome/test/chromedriver/chrome/stub_chrome.cc b/chrome/test/chromedriver/chrome/stub_chrome.cc
index 5e1cbe1e655e19eb457947d97dfc3a14e922b61a..394a1839baa551868dd40a314f0fb942898c4f1d 100644
--- a/chrome/test/chromedriver/chrome/stub_chrome.cc
+++ b/chrome/test/chromedriver/chrome/stub_chrome.cc
@@ -43,6 +43,10 @@ std::string StubChrome::GetOperatingSystemName() {
   return std::string();
 }
 
+bool StubChrome::IsMobileEmulationEnabled() const {
+  return false;
+}
+
 Status StubChrome::Quit() {
   return Status(kOk);
 }