Adding jobject null check before calling CalledByNative JNI functions

chrome/browser/android/tab_android.cc

Index: chrome/browser/android/tab_android.cc
diff --git a/chrome/browser/android/tab_android.cc b/chrome/browser/android/tab_android.cc
index baa0a000cb2aeef6856c7b08386b17534184d8da..076434444697a51418c59383d2d279837aa3cf43 100644
--- a/chrome/browser/android/tab_android.cc
+++ b/chrome/browser/android/tab_android.cc
@@ -208,20 +208,23 @@ void TabAndroid::SwapTabContents(content::WebContents* old_contents,
                                  bool did_start_load,
                                  bool did_finish_load) {
   JNIEnv* env = base::android::AttachCurrentThread();
+  ScopedJavaLocalRef<jobject> obj = weak_java_tab_.get(env);
+  if (obj.is_null())
+    return;
 
   // We need to notify the native InfobarContainer so infobars can be swapped.
   InfoBarContainerAndroid* infobar_container =
       reinterpret_cast<InfoBarContainerAndroid*>(
           Java_Tab_getNativeInfoBarContainer(
               env,
-              weak_java_tab_.get(env).obj()));
+              obj.obj()));
   InfoBarService* new_infobar_service =
       new_contents ? InfoBarService::FromWebContents(new_contents) : NULL;
   infobar_container->ChangeInfoBarManager(new_infobar_service);
 
   Java_Tab_swapWebContents(
       env,
-      weak_java_tab_.get(env).obj(),
+      obj.obj(),
       reinterpret_cast<intptr_t>(new_contents),
       did_start_load,
       did_finish_load);
@@ -231,6 +234,10 @@ void TabAndroid::Observe(int type,
                          const content::NotificationSource& source,
                          const content::NotificationDetails& details) {
   JNIEnv* env = base::android::AttachCurrentThread();
+  ScopedJavaLocalRef<jobject> obj = weak_java_tab_.get(env);

[Yaron, 2014/07/02 17:36:16]

I'm wondering about this one. Even if we don't have a java tab, two of the
notification types seemingly could function without hitting it. It's probably a
no-op cause the java tab is gone anyway but have you considered that case?

[Abhishek, 2014/07/02 19:44:56]

I think if java tab is gone, then there is no meaning of calling these
CalledByNative function for notifications(NOTIFICATION_FAVICON_UPDATED and
NOTIFICATION_NAV_ENTRY_CHANGED).

[Yaron, 2014/07/02 20:25:39]

Agreed. I was referring to NOTIFICATION_WEB_CONTENT_SETTINGS_CHANGED

It also seems likely to not have impact but I haven't traced it through to see
what would happen

[Abhishek, 2014/07/03 05:10:42]

Done.

+  if (obj.is_null())
+    return;
+
   switch (type) {
     case chrome::NOTIFICATION_WEB_CONTENT_SETTINGS_CHANGED: {
       TabSpecificContentSettings* settings =
@@ -253,10 +260,10 @@ void TabAndroid::Observe(int type,
       break;
     }
     case chrome::NOTIFICATION_FAVICON_UPDATED:
-      Java_Tab_onFaviconUpdated(env, weak_java_tab_.get(env).obj());
+      Java_Tab_onFaviconUpdated(env, obj.obj());
       break;
     case content::NOTIFICATION_NAV_ENTRY_CHANGED:
-      Java_Tab_onNavEntryChanged(env, weak_java_tab_.get(env).obj());
+      Java_Tab_onNavEntryChanged(env, obj.obj());
       break;
     default:
       NOTREACHED() << "Unexpected notification " << type;