Transfer serviceworker state during cross site navigations too.

base/id_map.h

Index: base/id_map.h
diff --git a/base/id_map.h b/base/id_map.h
index 9cbc1f8978fa8836b770f8370ff3b2a3f44e2017..bb47892c1e47dd31a57f81718b3d04684c3e96fb 100644
--- a/base/id_map.h
+++ b/base/id_map.h
@@ -53,7 +53,8 @@ class IDMap : public base::NonThreadSafe {
     Releaser<OS, 0>::release_all(&data_);
   }
 
-  // Sets whether Add should CHECK if passed in NULL data. Default is false.
+  // Sets whether Add and Replace should CHECK if passed in NULL data.
+  // Default is false.
   void set_check_on_null_data(bool value) { check_on_null_data_ = value; }
 
   // Adds a view with an automatically generated unique ID. See AddWithID.
@@ -94,6 +95,25 @@ class IDMap : public base::NonThreadSafe {
     }
   }
 
+  // Replaces the value for |id| with |new_data| and returns a pointer to the
+  // existing value. If there is no entry for |id|, the map is not altered and
+  // nullptr is returned. The OwnershipSemantics of the map have no affect on
+  // how the existing value is treated, the IDMap does not delete the existing
+  // value being replaced.
+  T* Replace(KeyType id, T* new_data) {
+    DCHECK(CalledOnValidThread());
+    CHECK(!check_on_null_data_ || new_data);
+    typename HashTable::iterator i = data_.find(id);
+    if (i == data_.end()) {
+      NOTREACHED() << "Attempting to replace an item not in the list";
+      return nullptr;
+    }
+
+    T* temp = i->second;
+    i->second = new_data;
+    return temp;
+  }
+
   void Clear() {
     DCHECK(CalledOnValidThread());
     if (iteration_depth_ == 0) {