[global] Remaps self.SDK.targetManager

This CL changes references to self.SDK.targetManager (the global
instance of SDK.SDKModel.TargetManager) over to
SDK.SDKModel.TargetManager.instance(). To keep both TypeScript and
Closure happy we must make a method on the TargetManager class itself,
since it only allows private constructors to be accessed by static
methods on the class.

Bug: 1058320
Change-Id: I6ca35024c21cf24254fd6273138a1ab3e163ee00
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2088092
Commit-Queue: Paul Lewis <[email protected]>
Reviewed-by: Tim van der Lippe <[email protected]>
diff --git a/front_end/network/BlockedURLsPane.js b/front_end/network/BlockedURLsPane.js
index 948ec79..b269d9cc 100644
--- a/front_end/network/BlockedURLsPane.js
+++ b/front_end/network/BlockedURLsPane.js
@@ -47,7 +47,7 @@
 
     /** @type {!Map<string, number>} */
     this._blockedCountForUrl = new Map();
-    self.SDK.targetManager.addModelListener(
+    SDK.SDKModel.TargetManager.instance().addModelListener(
         SDK.NetworkManager.NetworkManager, SDK.NetworkManager.Events.RequestFinished, this._onRequestFinished, this);
 
     this._updateThrottler = new Common.Throttler.Throttler(200);