[Document mode] Allow multiple popup windows to appear.

chrome/android/java/src/org/chromium/chrome/browser/tabmodel/document/ActivityDelegate.java

Index: chrome/android/java/src/org/chromium/chrome/browser/tabmodel/document/ActivityDelegate.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/tabmodel/document/ActivityDelegate.java b/chrome/android/java/src/org/chromium/chrome/browser/tabmodel/document/ActivityDelegate.java
index 6e335747cf499238449c29497abb19af9f6028e1..b6d91af77f9f66e7444e9f26206dc38c924e560a 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/tabmodel/document/ActivityDelegate.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/tabmodel/document/ActivityDelegate.java
@@ -16,6 +16,7 @@ import android.os.Build;
 import android.text.TextUtils;
 
 import org.chromium.base.ApplicationStatus;
+import org.chromium.chrome.browser.ChromeActivity;
 import org.chromium.chrome.browser.Tab;
 import org.chromium.chrome.browser.UrlConstants;
 import org.chromium.chrome.browser.document.DocumentActivity;
@@ -204,4 +205,19 @@ public class ActivityDelegate {
         }
         return false;
     }
-}
+
+    /** @return Running Activity that owns the given Tab, null if the Activity couldn't be found. */
+    public static Activity getActivityForTabId(int id) {
+        if (id == Tab.INVALID_TAB_ID) return null;
+
+        for (WeakReference<Activity> ref : ApplicationStatus.getRunningActivities()) {
+            if (!(ref.get() instanceof ChromeActivity)) continue;
+
+            ChromeActivity activity = (ChromeActivity) ref.get();
+            if (activity == null) continue;
+
+            if (activity.getTabModelSelector().getTabById(id) != null) return activity;
+        }
+        return null;
+    }
+}