Add a field + getter for instanceKey to ReactContext

Summary:
Adding a new String field for `instanceKey` to ReactContext, which is set via a new constructor on ReactApplicationContext. Also adding getters to ReactContext and ThemedReactContext so that it's accessible from any instance/subclass of ReactContext.

This will only be used in bridgeless mode.

Reviewed By: mdvacca

Differential Revision: D18316556

fbshipit-source-id: 9757da72fde4ba36034c1e129326461fed496229

ReactAndroid/src/main/java/com/facebook/react/bridge/ReactApplicationContext.java

@@ -20,4 +20,15 @@ public class ReactApplicationContext extends ReactContext {
   public ReactApplicationContext(Context context) {
     super(context.getApplicationContext());
   }
+
+  /**
+   * A constructor that takes a unique string identifier for the React instance. For bridgeless mode
+   * only - do not use.
+   *
+   * <p>TODO T43898341 Make this package-private once we've consolidated the classes that need this
+   * in this package
+   */
+  public ReactApplicationContext(Context context, String instanceKey) {
+    super(context.getApplicationContext(), instanceKey);
+  }
 }

ReactAndroid/src/main/java/com/facebook/react/bridge/ReactContext.java

@@ -53,9 +53,20 @@ public class ReactContext extends ContextWrapper {
   private @Nullable NativeModuleCallExceptionHandler mNativeModuleCallExceptionHandler;
   private @Nullable NativeModuleCallExceptionHandler mExceptionHandlerWrapper;
   private @Nullable WeakReference<Activity> mCurrentActivity;
+  private final @Nullable String mInstanceKey;
 
   public ReactContext(Context base) {
     super(base);
+    mInstanceKey = null;
+  }
+
+  /**
+   * A constructor that takes a unique string identifier for the React instance. For bridgeless mode
+   * only - do not use.
+   */
+  /* package */ ReactContext(Context base, String instanceKey) {
+    super(base);
+    mInstanceKey = instanceKey;
   }
 
   /** Set and initialize CatalystInstance for this Context. This should be called exactly once. */
@@ -408,4 +419,14 @@ public class ReactContext extends ContextWrapper {
   public JavaScriptContextHolder getJavaScriptContextHolder() {
     return mCatalystInstance.getJavaScriptContextHolder();
   }
+
+  /**
+   * TODO T43898341 Make this package-private once we've consolidated the classes that need this in
+   * this package
+   *
+   * @return The key for the associated React instance
+   */
+  public @Nullable String getInstanceKey() {
+    return mInstanceKey;
+  }
 }

ReactAndroid/src/main/java/com/facebook/react/uimanager/ThemedReactContext.java

@@ -53,4 +53,10 @@ public class ThemedReactContext extends ReactContext {
   public @Nullable Activity getCurrentActivity() {
     return mReactApplicationContext.getCurrentActivity();
   }
+
+  @Nullable
+  @Override
+  public String getInstanceKey() {
+    return mReactApplicationContext.getInstanceKey();
+  }
 }