Make multiple calls to DialogOverlayImpl.close() do nothing.

content/public/android/java/src/org/chromium/content/browser/androidoverlay/DialogOverlayImpl.java

Index: content/public/android/java/src/org/chromium/content/browser/androidoverlay/DialogOverlayImpl.java
diff --git a/content/public/android/java/src/org/chromium/content/browser/androidoverlay/DialogOverlayImpl.java b/content/public/android/java/src/org/chromium/content/browser/androidoverlay/DialogOverlayImpl.java
index 52d90d2fbc8d8e92921123ca4cba2b57f6771731..2163346f4982384c6306acdc0311a97a1532dc83 100644
--- a/content/public/android/java/src/org/chromium/content/browser/androidoverlay/DialogOverlayImpl.java
+++ b/content/public/android/java/src/org/chromium/content/browser/androidoverlay/DialogOverlayImpl.java
@@ -42,6 +42,9 @@ public class DialogOverlayImpl implements AndroidOverlay, DialogOverlayCore.Host
     // If nonzero, then we have registered a surface with this ID.
     private int mSurfaceId;
 
+    // Has close() been run yet?
+    private boolean mClosed;
+
     /**
      * @param client Mojo client interface.
      * @param config initial overlay configuration.
@@ -81,6 +84,10 @@ public class DialogOverlayImpl implements AndroidOverlay, DialogOverlayCore.Host
     public void close() {
         ThreadUtils.assertOnUiThread();
 
+        if (mClosed) return;
+
+        mClosed = true;
+
         // TODO(liberato): verify that this actually works, else add an explicit shutdown and hope
         // that the client calls it.