Add attachToWindow event to infobar observer

chrome/android/java/src/org/chromium/chrome/browser/infobar/InfoBarContainer.java

Index: chrome/android/java/src/org/chromium/chrome/browser/infobar/InfoBarContainer.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/infobar/InfoBarContainer.java b/chrome/android/java/src/org/chromium/chrome/browser/infobar/InfoBarContainer.java
index 3f773de0533259e815bc446e6f367372ddc1ac52..68d8fd20dff3965e9169d7207e555ce746b62137 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/infobar/InfoBarContainer.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/infobar/InfoBarContainer.java
@@ -78,6 +78,12 @@ public class InfoBarContainer extends SwipableOverlayView {
          * @param isLast Whether the infobar container is going to be empty
          */
         void onRemoveInfoBar(InfoBarContainer container, InfoBar infoBar, boolean isLast);
+
+        /**
+         * Called when the InfobarContainer is attached to the window.
+         * @param hasInfobars True if infobar container has infobars to show.
+         */
+        void onInfoBarContainerAttachedToWindow(boolean hasInfobars);
     }
 
     /** Toggles visibility of the InfoBarContainer when the keyboard appears. */
@@ -354,6 +360,10 @@ public class InfoBarContainer extends SwipableOverlayView {
             setAlpha(0f);
             animate().alpha(1f).setDuration(REATTACH_FADE_IN_MS);
         }
+        // Notify observers that the container has attached to the window.
+        for (InfoBarContainerObserver observer : mObservers) {
+            observer.onInfoBarContainerAttachedToWindow(!mInfoBars.isEmpty());
+        }
     }
 
     private native long nativeInit();