[Android] Reland CommandLine reset listeners.

base/android/java/src/org/chromium/base/CommandLine.java

Index: base/android/java/src/org/chromium/base/CommandLine.java
diff --git a/base/android/java/src/org/chromium/base/CommandLine.java b/base/android/java/src/org/chromium/base/CommandLine.java
index 9f5407921a9fd492f760d9e9ab2875cc99dcb5a8..409329cfabf8ec6b05adec145155e75f3e973ad8 100644
--- a/base/android/java/src/org/chromium/base/CommandLine.java
+++ b/base/android/java/src/org/chromium/base/CommandLine.java
@@ -16,6 +16,7 @@ import java.io.Reader;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
+import java.util.List;
 import java.util.concurrent.atomic.AtomicReference;
 
 /**
@@ -25,6 +26,15 @@ import java.util.concurrent.atomic.AtomicReference;
  * ContentShellApplication.COMMAND_LINE_FILE or ChromeShellApplication.COMMAND_LINE_FILE.
 **/
 public abstract class CommandLine {
+    /**
+     * Allows classes who cache command line flags to be notified when those arguments are updated
+     * at runtime. This happens in tests.
+     */
+    public interface ResetListener {
+        /** Called when the command line arguments are reset. */
+        void onCommandLineReset();
+    }
+
     // Public abstract interface, implemented in derived classes.
     // All these methods reflect their native-side counterparts.
     /**
@@ -87,6 +97,7 @@ public abstract class CommandLine {
         return false;
     }
 
+    private static final List<ResetListener> sResetListeners = new ArrayList<>();
     private static final AtomicReference<CommandLine> sCommandLine =
             new AtomicReference<CommandLine>();
 
@@ -132,6 +143,20 @@ public abstract class CommandLine {
     @VisibleForTesting
     public static void reset() {
         setInstance(null);
+        ThreadUtils.postOnUiThread(new Runnable() {
+            @Override
+            public void run() {
+                for (ResetListener listener : sResetListeners) listener.onCommandLineReset();
+            }
+        });
+    }
+
+    public static void addResetListener(ResetListener listener) {
+        sResetListeners.add(listener);
+    }
+
+    public static void removeResetListener(ResetListener listener) {
+        sResetListeners.remove(listener);
     }
 
     /**