Bug 1647883: Part 1 - Remove hashCode and equals overrides from Gecko…

…Session in favour of new, package-scoped GeckoSession.equalsId method; r=geckoview-reviewers,agi

Because `GeckoSession`'s overrides of `hashCode` and `equals` look solely at session ID, this may cause
strange behaviors if a `GeckoSession` is reloaded with session state from a previous instance, and the
previous instance still exists. For example, suppose the previous instance is closed and the new instance is
open. As far as the Android runtime is concerned, both objects are equivalent. Trying to insert both objects
into the same container will not work as expected.

In this patch, we revert those overrides. To ensure that we still have a short-circuit path in
`GeckoView.restoreSession`, we add and utilize a new, `package`-scoped, `equalsId` method.

Differential Revision: https://phabricator.services.mozilla.com/D81746

mobile/android/geckoview/src/main/java/org/mozilla/geckoview/GeckoSession.java

@@ -1333,16 +1333,12 @@ public GeckoSession[] newArray(final int size) {
         }
     };
 
-    @Override
-    @AnyThread
-    public int hashCode() {
-        return mId.hashCode();
-    }
+    /* package */ boolean equalsId(final GeckoSession other) {
+        if (other == null) {
+            return false;
+        }
 
-    @Override
-    @AnyThread
-    public boolean equals(final Object obj) {
-        return obj instanceof GeckoSession && mId.equals(((GeckoSession) obj).mId);
+        return mId.equals(other.mId);
     }
 
     /**

mobile/android/geckoview/src/main/java/org/mozilla/geckoview/GeckoView.java

@@ -585,7 +585,7 @@ protected void onRestoreInstanceState(final Parcelable state) {
     }
 
     private void restoreSession(final @Nullable GeckoSession savedSession) {
-        if (savedSession == null || savedSession.equals(mSession)) {
+        if (savedSession == null || savedSession.equalsId(mSession)) {
             return;
         }
 

mobile/android/geckoview/src/main/java/org/mozilla/geckoview/doc-files/CHANGELOG.md

@@ -13,6 +13,10 @@ exclude: true
 
 ⚠️  breaking change and deprecation notices
 
+## v80
+- Removed `GeckoSession.hashCode` and `GeckoSession.equals` overrides in favor
+  of the default implementations. ([bug 1647883]({{bugzilla}}1647883))
+
 ## v79
 - Added `runtime.openOptionsPage` support. For `options_ui.open_in_new_tab` ==
   `false`, [`TabDelegate.onOpenOptionsPage`][79.1] is called.