Delete tab state files when the user explicitly closes a CCT.

chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabTabPersistencePolicy.java

Index: chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabTabPersistencePolicy.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabTabPersistencePolicy.java b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabTabPersistencePolicy.java
index 58e6efe1806c733ee1b7a0681f5042add97985c0..2c787bab37eeb76384d28a572e4ffe089e9dc8f6 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabTabPersistencePolicy.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabTabPersistencePolicy.java
@@ -205,6 +205,22 @@ public class CustomTabTabPersistencePolicy implements TabPersistencePolicy {
     }
 
     /**
+     * Triggers an async deletion of the tab state metadata file.
+     */
+    public void deleteMetadataStateFileAsync() {
+        AsyncTask.SERIAL_EXECUTOR.execute(new Runnable() {
+            @Override
+            public void run() {
+                File stateDir = getOrCreateStateDirectory();
+                File metadataFile = new File(stateDir, getStateFileName());
+                if (metadataFile.exists() && !metadataFile.delete()) {
+                    Log.e(TAG, "Failed to delete file: " + metadataFile);
+                }
+            }
+        });
+    }
+
+    /**
      * Given a list of metadata files, determine which are applicable for deletion based on the
      * deletion strategy of Custom Tabs.
      *