Adding jobject null check before calling CalledByNative JNI functions

chrome/browser/android/tab_android.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/android/tab_android.h"
 
 #include "base/android/jni_android.h"
 #include "base/android/jni_array.h"
 #include "base/android/jni_string.h"
 #include "base/debug/trace_event.h"
@@ skipping 190 matching lines @@
     }
   }
   return false;
 }
 
 void TabAndroid::SwapTabContents(content::WebContents* old_contents,
                                  content::WebContents* new_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);
 }
 
 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 =
           TabSpecificContentSettings::FromWebContents(web_contents());
       if (!settings->IsBlockageIndicated(CONTENT_SETTINGS_TYPE_POPUPS)) {
         // TODO(dfalcantara): Create an InfoBarDelegate to keep the
         // PopupBlockedInfoBar logic native-side instead of straddling the JNI
         // boundary.
         int num_popups = 0;
         PopupBlockerTabHelper* popup_blocker_helper =
             PopupBlockerTabHelper::FromWebContents(web_contents());
         if (popup_blocker_helper)
           num_popups = popup_blocker_helper->GetBlockedPopupsCount();
 
         if (num_popups > 0)
           PopupBlockedInfoBarDelegate::Create(web_contents(), num_popups);
 
         settings->SetBlockageHasBeenIndicated(CONTENT_SETTINGS_TYPE_POPUPS);
       }
       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;
       break;
   }
 }
 
 void TabAndroid::Destroy(JNIEnv* env, jobject obj) {
   delete this;
 }
@@ skipping 256 matching lines @@
 
 static void Init(JNIEnv* env, jobject obj) {
   TRACE_EVENT0("native", "TabAndroid::Init");
   // This will automatically bind to the Java object and pass ownership there.
   new TabAndroid(env, obj);
 }
 
 bool TabAndroid::RegisterTabAndroid(JNIEnv* env) {
   return RegisterNativesImpl(env);
 }