[Android] Zero out infobar native pointer after destruction

This properly prevents double destruction as intended by the
surrounding if block.

R=mdjones@chromium.org

Bug: None
Change-Id: I97c9d13098bfb01df99a65a55e274ebf1e8d1a07
Reviewed-on: https://chromium-review.googlesource.com/c/1309098Reviewed-by: Matthew Jones <mdjones@chromium.org>
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604375}

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

@@ -130,8 +130,10 @@ public class InfoBarContainer extends SwipableOverlayView implements UserData {
             WebContents webContents = tab.getWebContents();
             if (webContents != null && webContents != getWebContents()) {
                 setWebContents(webContents);
+                if (mNativeInfoBarContainer != 0) {
                     nativeSetWebContents(mNativeInfoBarContainer, webContents);
                 }
+            }
 
             mTabView.removeOnAttachStateChangeListener(mAttachedStateListener);
             mTabView = tab.getView();
@@ -170,12 +172,12 @@ public class InfoBarContainer extends SwipableOverlayView implements UserData {
     /** Helper class to manage showing in-product help bubbles over specific info bars. */
     private final IPHInfoBarSupport mIPHSupport;
 
-    /** Native InfoBarContainer pointer which will be set by nativeInit(). */
-    private final long mNativeInfoBarContainer;
-
     /** The list of all InfoBars in this container, regardless of whether they've been shown yet. */
     private final ArrayList<InfoBar> mInfoBars = new ArrayList<InfoBar>();
 
+    /** Native InfoBarContainer pointer which will be set by nativeInit(). */
+    private long mNativeInfoBarContainer;
+
     /** True when this container has been emptied and its native counterpart has been destroyed. */
     private boolean mDestroyed;
 
@@ -429,6 +431,7 @@ public class InfoBarContainer extends SwipableOverlayView implements UserData {
         mDestroyed = true;
         if (mNativeInfoBarContainer != 0) {
             nativeDestroy(mNativeInfoBarContainer);
+            mNativeInfoBarContainer = 0;
         }
     }