Use task id to determine if Preferences should be finished

Use the taskId rather to determine if finish() should be called
on Preferences. Previously, if a user navigated in Preferences,
sResumedInstance got set to the sub-Preference and the main
Preference got finished. Since they belong to the same task, this
shouldn't happen.

BUG=652572

Review-Url: https://codereview.chromium.org/2386213004
Cr-Commit-Position: refs/heads/master@{#422862}

chrome/android/java/src/org/chromium/chrome/browser/preferences/Preferences.java

@@ -157,13 +157,16 @@ public class Preferences extends AppCompatActivity implements
 
         // Prevent the user from interacting with multiple instances of Preferences at the same time
         // (e.g. in multi-instance mode on a Samsung device), which would cause many fun bugs.
-        if (sResumedInstance != null && sResumedInstance != this && !mIsNewlyCreated) {
+        if (sResumedInstance != null && sResumedInstance.getTaskId() != getTaskId()
+                && !mIsNewlyCreated) {
             // This activity was unpaused or recreated while another instance of Preferences was
             // already showing. The existing instance takes precedence.
             finish();
         } else {
             // This activity was newly created and takes precedence over sResumedInstance.
-            if (sResumedInstance != null && sResumedInstance != this) sResumedInstance.finish();
+            if (sResumedInstance != null && sResumedInstance.getTaskId() != getTaskId()) {
+                sResumedInstance.finish();
+            }
 
             sResumedInstance = this;
             mIsNewlyCreated = false;