DevTools: Use JS symbols instead of strings for eligible events.

third_party/WebKit/Source/devtools/front_end/sdk/NetworkManager.js

Index: third_party/WebKit/Source/devtools/front_end/sdk/NetworkManager.js
diff --git a/third_party/WebKit/Source/devtools/front_end/sdk/NetworkManager.js b/third_party/WebKit/Source/devtools/front_end/sdk/NetworkManager.js
index 811ee9bc6590a482b990a88770b7ddd52f3f7e93..551b1e2e913ddae3aae149b74a845178c5d379d6 100644
--- a/third_party/WebKit/Source/devtools/front_end/sdk/NetworkManager.js
+++ b/third_party/WebKit/Source/devtools/front_end/sdk/NetworkManager.js
@@ -733,9 +733,10 @@ WebInspector.MultitargetNetworkManager = function()
     this._networkConditions = WebInspector.NetworkManager.NoThrottlingConditions;
 }
 
+/** @enum {symbol} */
 WebInspector.MultitargetNetworkManager.Events = {
-    ConditionsChanged: "ConditionsChanged",
-    UserAgentChanged: "UserAgentChanged"
+    ConditionsChanged: Symbol("ConditionsChanged"),
+    UserAgentChanged: Symbol("UserAgentChanged")
 }
 
 WebInspector.MultitargetNetworkManager.prototype = {