Remove one thread hop while fetching matching rules

chrome/browser/android/data_usage/data_use_tab_model.h

Index: chrome/browser/android/data_usage/data_use_tab_model.h
diff --git a/chrome/browser/android/data_usage/data_use_tab_model.h b/chrome/browser/android/data_usage/data_use_tab_model.h
index d1680993d81c0044c69aae61ff4c97c888e62548..a6ada48050d2437c7c11931c4615e23fee1d677c 100644
--- a/chrome/browser/android/data_usage/data_use_tab_model.h
+++ b/chrome/browser/android/data_usage/data_use_tab_model.h
@@ -21,20 +21,19 @@
 #include "base/time/time.h"
 #include "chrome/browser/android/data_usage/tab_data_use_entry.h"
 #include "components/sessions/core/session_id.h"
+#include "url/gurl.h"
 
 namespace base {
 class SingleThreadTaskRunner;
 class TickClock;
 }
 
-class GURL;
-
 namespace chrome {
 
 namespace android {
 
 class DataUseMatcher;
-class ExternalDataUseObserver;
+class ExternalDataUseObserverBridge;
 
 // Models tracking and labeling of data usage within each Tab. Within each tab,
 // the model tracks the data use of a sequence of navigations in a "tracking
@@ -85,11 +84,10 @@ class DataUseTabModel {
 
   DataUseTabModel();
 
-  // Initializes |this| on UI thread. |external_data_use_observer| is the weak
-  // pointer to ExternalDataUseObserver object that owns |this|.
+  // Initializes |this| on UI thread. |external_data_use_observer_bridge| is the
+  // pointer to ExternalDataUseObserverBridge object.

[tbansal1, 2016/03/08 18:15:01]

say more about ownership and lifetime: It seems the caller owns the bridge
object, but I am not sure if the bridge can get destroyed before |this|?

[Raj, 2016/03/09 02:27:35]

Done.

   void InitOnUIThread(
-      const scoped_refptr<base::SingleThreadTaskRunner>& io_task_runner,
-      const base::WeakPtr<ExternalDataUseObserver>& external_data_use_observer);
+      const ExternalDataUseObserverBridge* external_data_use_observer_bridge);
 
   virtual ~DataUseTabModel();
 
@@ -196,6 +194,14 @@ class DataUseTabModel {
 
   typedef base::hash_map<SessionID::id_type, TabDataUseEntry> TabEntryMap;
 
+  // Contains the details of a single UI navigation event.
+  struct DataUseUINavigationBuffer {

[tbansal1, 2016/03/08 18:15:00]

This name seems incorrect. This is not a buffer/collection, more like a single
event.

+    SessionID::id_type tab_id;
+    TransitionType transition;

[tbansal1, 2016/03/08 18:15:01]

s/transition/transition_type/

+    GURL url;
+    std::string package;

[tbansal1, 2016/03/08 18:15:01]

nit: may be add comments for the fields. e.g., is the package name of the
package that started this navigation?

+  };
+
   // Gets the current label of a tab, and the new label if a navigation event
   // occurs in the tab. |tab_id| is the source tab of the generated event,
   // |transition| indicates the type of the UI event/transition,  |url| is the
@@ -231,6 +237,8 @@ class DataUseTabModel {
   // size is |kMaxTabEntries|.
   void CompactTabEntries();
 
+  void ProcessBufferedNavigationEvents();

[tbansal1, 2016/03/08 18:15:01]

function comments.

+
   // Collection of observers that receive tracking session start and end
   // notifications. Notifications are posted on UI thread.
   base::ObserverList<TabDataUseObserver> observers_;
@@ -258,6 +266,12 @@ class DataUseTabModel {
   // True if the external control app is installed.
   bool is_control_app_installed_;
 
+  // Buffers the list of UI navigation events that occurred until the first rule
+  // fetch is complete or the control app not installed callback was received or
+  // until |kDefaultMaxNavigationEventsBuffered| navigation events were
+  // buffered.
+  scoped_ptr<std::vector<DataUseUINavigationBuffer>> ui_navigation_buffer;

[tbansal1, 2016/03/08 18:15:00]

s/ui_navigation_buffer/data_use_ui_navigations_/?

[tbansal1, 2016/03/08 18:15:01]

Also, why does this need to be a scoped_ptr, and not a regular variable
std::vector<...> ui_navigation_buffer_;

May be add another variable
bool buffer_navigations_
instead of overriding this variable.

[tbansal1, 2016/03/08 18:15:01]

variable name should end with underscore.

[tbansal1, 2016/03/08 18:15:01]

say more about this buffer: what is the order in which events are stored. It
seems they are stored in FIFO?

+
   base::ThreadChecker thread_checker_;
 
   base::WeakPtrFactory<DataUseTabModel> weak_factory_;