remove activities from module constructors

Summary:
Refactor modules that take activities (or activities that implement some interface) as constructor args to not do that. Expose `getCurrentActivity()` in `ReactContext` and use that wherever the activity is needed.

public

Reviewed By: astreet

Differential Revision: D2680462

fb-gh-sync-id: f263b3fe5b422b7aab9fdadd051cef4e82797b0a

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

@@ -146,7 +146,6 @@ public class ReactContext extends ContextWrapper {
    */
   public void onPause() {
     UiThreadUtil.assertOnUiThread();
-    mCurrentActivity = null;
     for (LifecycleEventListener listener : mLifecycleEventListeners) {
       listener.onHostPause();
     }
@@ -163,6 +162,7 @@ public class ReactContext extends ContextWrapper {
     if (mCatalystInstance != null) {
       mCatalystInstance.destroy();
     }
+    mCurrentActivity = null;
   }
 
   /**
@@ -239,4 +239,13 @@ public class ReactContext extends ContextWrapper {
     mCurrentActivity.startActivityForResult(intent, code, bundle);
     return true;
   }
+
+  /**
+   * Get the activity to which this context is currently attached, or {@code null} if not attached.
+   * DO NOT HOLD LONG-LIVED REFERENCES TO THE OBJECT RETURNED BY THIS METHOD, AS THIS WILL CAUSE
+   * MEMORY LEAKS.
+   */
+  /* package */ @Nullable Activity getCurrentActivity() {
+    return mCurrentActivity;
+  }
 }