[Topics] Organize Taxonomy v1 as a Semantic Tree

Use this tree to filter topics by observers who viewed topic descendants instead of using a child-to-parent map. Use this tree as the source of truth for a topic's name.

This change will support adding new taxonomies.

Binary-Size: Size increase is unavoidable
Change-Id: I9991053a8a0f8d5ed6f3974a46e6d10c2d6cbb75
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4330034
Reviewed-by: Yao Xiao <yaoxia@chromium.org>
Reviewed-by: Josh Karlin <jkarlin@chromium.org>
Reviewed-by: Theodore Olsauskas-Warren <sauski@google.com>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1119815}

components/BUILD.gn

@@ -336,6 +336,7 @@ test("components_unittests") {
       "//components/blocked_content:unit_tests",
       "//components/browsing_data/content:unit_tests",
       "//components/browsing_topics:unit_tests",
+      "//components/browsing_topics/common:unit_tests",
       "//components/captive_portal/content:unit_tests",
       "//components/cast_receiver:unit_tests",
       "//components/cast_streaming:unit_tests",

components/browsing_topics/BUILD.gn

@@ -71,7 +71,6 @@ source_set("unit_tests") {
     "browsing_topics_state_unittest.cc",
     "epoch_topics_unittest.cc",
     "topic_and_domains_unittest.cc",
-    "util_unittest.cc",
   ]
 
   deps = [

components/browsing_topics/browsing_topics_calculator.cc

@@ -9,7 +9,7 @@
 #include "base/rand_util.h"
 #include "base/ranges/algorithm.h"
 #include "base/task/single_thread_task_runner.h"
-#include "components/browsing_topics/util.h"
+#include "components/browsing_topics/common/semantic_tree.h"
 #include "components/history/core/browser/history_service.h"
 #include "components/optimization_guide/content/browser/page_content_annotations_service.h"
 #include "components/privacy_sandbox/canonical_topic.h"
@@ -444,8 +444,7 @@ void BrowsingTopicsCalculator::OnGetTopicsForHostsCompleted(
   // For each top topic, derive the context domains that observed it
   std::vector<TopicAndDomains> top_topics_and_observing_domains;
 
-  const std::map<Topic, std::vector<Topic>> parent_to_child_topic_map =
-      GetParentToChildTopicMap();
+  SemanticTree semantic_tree;
 
   for (const Topic& topic : top_topics) {
     if (!privacy_sandbox_settings_->IsTopicAllowed(
@@ -462,7 +461,7 @@ void BrowsingTopicsCalculator::OnGetTopicsForHostsCompleted(
 
     // Calculate descendant topics + their observing context domains
     std::set<Topic> descendant_topics =
-        GetDescendantTopics(topic, parent_to_child_topic_map);
+        semantic_tree.GetDescendantTopics(topic);
     for (const Topic& descendant_topic : descendant_topics) {
       std::set<HashedDomain> descendant_topic_observation_domains =
           GetTopicObservationDomains(descendant_topic, topic_hosts_map,

components/browsing_topics/common/BUILD.gn

@@ -10,7 +10,23 @@ component("common") {
   sources = [
     "common_types.cc",
     "common_types.h",
+    "semantic_tree.cc",
+    "semantic_tree.h",
   ]
 
-  deps = [ "//base" ]
+  deps = [
+    "//base",
+    "//components/strings:components_strings_grit",
+  ]
+}
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [ "semantic_tree_unittest.cc" ]
+
+  deps = [
+    ":common",
+    "//base/test:test_support",
+    "//components/strings:components_strings_grit",
+  ]
 }

components/browsing_topics/common/DEPS

@@ -0,0 +1,3 @@
+include_rules = [
+  "+components/strings/grit/components_strings.h",
+]