Fix buggy use of memset in Rankings::Iterator

Using memset over this causes the raw_ptr's private ptr to be reset
incorrectly, without updating the refcount. It causes the quarantine size to increase infinitely.

This patch is likely to be merged into beta, so I made the minimal
change. I would like to refactor this more in a second step.

Plan:
1. Minimal fix (this patch)
2. Refactor: https://chromium-review.googlesource.com/c/chromium/src/+/4189439

Bug: 1409814
Change-Id: I0f7f057fe04ac5e90e9f720473c03521752e0db7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4188566
Reviewed-by: Josh Karlin <jkarlin@chromium.org>
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1096455}

net/disk_cache/blockfile/rankings.cc

@@ -206,9 +206,7 @@ Rankings::ScopedRankingsBlock::ScopedRankingsBlock(Rankings* rankings,
                                                    CacheRankingsBlock* node)
     : std::unique_ptr<CacheRankingsBlock>(node), rankings_(rankings) {}
 
-Rankings::Iterator::Iterator() {
-  memset(this, 0, sizeof(Iterator));
-}
+Rankings::Iterator::Iterator() = default;
 
 void Rankings::Iterator::Reset() {
   if (my_rankings) {
@@ -216,7 +214,9 @@ void Rankings::Iterator::Reset() {
       ScopedRankingsBlock(my_rankings, node);
     }
   }
-  memset(this, 0, sizeof(Iterator));
+  my_rankings = nullptr;
+  nodes = {nullptr, nullptr, nullptr};
+  list = List::NO_USE;
 }
 
 Rankings::Rankings() = default;

net/disk_cache/blockfile/rankings.h

@@ -10,6 +10,7 @@
 #include <list>
 #include <memory>
 
+#include <array>
 #include "base/memory/raw_ptr.h"
 #include "net/disk_cache/blockfile/addr.h"
 #include "net/disk_cache/blockfile/mapped_file.h"
@@ -96,13 +97,17 @@ class Rankings {
 
   // If we have multiple lists, we have to iterate through all at the same time.
   // This structure keeps track of where we are on the iteration.
+  // TODO(https://crbug.com/1409814) refactor this struct to make it clearer
+  // this owns the `nodes`.
   struct Iterator {
     Iterator();
     void Reset();
 
-    List list;                     // Which entry was returned to the user.
-    CacheRankingsBlock* nodes[3];  // Nodes on the first three lists.
-    raw_ptr<Rankings> my_rankings;
+    // Which entry was returned to the user.
+    List list = List::NO_USE;
+    // Nodes on the first three lists.
+    std::array<CacheRankingsBlock*, 3> nodes = {nullptr, nullptr, nullptr};
+    raw_ptr<Rankings> my_rankings = nullptr;
   };
 
   Rankings();