Replace TOUCH_UI condition in WebUI with dynamic flag.

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index 80e45d08c8d86c5de067f7ef7ca31ea18205d61c..16190b5a0b24110d959cadcdc82eaf576762f5ba 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -1062,6 +1062,9 @@ const char kTestType[]                      = "test-type";
 // channel with the given ID.
 const char kTestingChannelID[]              = "testing-channel";
 
+// Enables UI changes that make it easier to use with a touchscreen.
+const char kTouchOptimizedUI[]              = "touch-optimized-ui";
+
 // Experimental. Shows a dialog asking the user to try chrome. This flag is to
 // be used only by the upgrade process.
 const char kTryChromeAgain[]                = "try-chrome-again";