predictors: Take the priority into account for scoring resources.

This changes the way the resource score is computed in the
resource_prefetch_predictor. It takes into account the request priority
as the most important feature, then resource type, then average position.

The rationale is that resource priority surfaces the render-blocking
resources, that are the most critical to prefetch.

BUG=631966

Review-Url: https://codereview.chromium.org/2385173002
Cr-Commit-Position: refs/heads/master@{#422753}

chrome/browser/predictors/resource_prefetch_predictor_tables.cc

@@ -134,6 +134,7 @@ void ResourcePrefetchPredictorTables::SortResources(
     std::vector<ResourceData>* resources) {
   std::sort(resources->begin(), resources->end(),
             [](const ResourceData& x, const ResourceData& y) {
+              // Decreasing score ordering.
               return ComputeResourceScore(x) > ComputeResourceScore(y);
             });
 }
@@ -143,6 +144,7 @@ void ResourcePrefetchPredictorTables::SortRedirects(
     std::vector<RedirectStat>* redirects) {
   std::sort(redirects->begin(), redirects->end(),
             [](const RedirectStat& x, const RedirectStat& y) {
+              // Decreasing score ordering.
               return ComputeRedirectScore(x) > ComputeRedirectScore(y);
             });
 }
@@ -478,21 +480,46 @@ bool ResourcePrefetchPredictorTables::StringsAreSmallerThanDBLimit(
 // static
 float ResourcePrefetchPredictorTables::ComputeResourceScore(
     const ResourceData& data) {
-  // The score is calculated so that when the rows are sorted, stylesheets,
-  // scripts and fonts appear first, sorted by position(ascending) and then the
-  // rest of the resources sorted by position (ascending).
-  static const int kMaxResourcesPerType = 100;
+  // The ranking is done by considering, in this order:
+  // 1. Resource Priority
+  // 2. Request resource type
+  // 3. Finally, the average position, giving a higher priotity to earlier
+  //    resources.
+
+  int priority_multiplier;
+  switch (data.priority()) {
+    case ResourceData::REQUEST_PRIORITY_HIGHEST:
+      priority_multiplier = 3;
+      break;
+    case ResourceData::REQUEST_PRIORITY_MEDIUM:
+      priority_multiplier = 2;
+      break;
+    case ResourceData::REQUEST_PRIORITY_LOW:
+    case ResourceData::REQUEST_PRIORITY_LOWEST:
+    case ResourceData::REQUEST_PRIORITY_IDLE:
+    default:
+      priority_multiplier = 1;
+      break;
+  }
+
+  int type_multiplier;
   switch (data.resource_type()) {
     case ResourceData::RESOURCE_TYPE_STYLESHEET:
     case ResourceData::RESOURCE_TYPE_SCRIPT:
+      type_multiplier = 3;
+      break;
     case ResourceData::RESOURCE_TYPE_FONT_RESOURCE:
-      return (2 * kMaxResourcesPerType) - data.average_position();
-
+      type_multiplier = 2;
+      break;
     case ResourceData::RESOURCE_TYPE_IMAGE:
     default:
-      return kMaxResourcesPerType - data.average_position();
+      type_multiplier = 1;
   }
-  // TODO(lizeb): Take priority into account.
+
+  constexpr int kMaxResourcesPerType = 100;
+  return kMaxResourcesPerType *
+             (priority_multiplier * 100 + type_multiplier * 10) -
+         data.average_position();
 }
 
 // static

chrome/browser/predictors/resource_prefetch_predictor_tables_unittest.cc

@@ -575,33 +575,47 @@ void ResourcePrefetchPredictorTablesTest::ReopenDatabase() {
 // Test cases.
 
 TEST_F(ResourcePrefetchPredictorTablesTest, ComputeResourceScore) {
-  ResourceData js_resource = CreateResourceData(
-      "http://www.resources.google.com/script.js",
-      content::RESOURCE_TYPE_SCRIPT, 11, 0, 0, 1., net::MEDIUM, false, false);
-  ResourceData image_resource = CreateResourceData(
-      "http://www.resources.google.com/image.jpg", content::RESOURCE_TYPE_IMAGE,
-      11, 0, 0, 1., net::MEDIUM, false, false);
-  ResourceData css_resource =
-      CreateResourceData("http://www.resources.google.com/stylesheet.css",
-                         content::RESOURCE_TYPE_STYLESHEET, 11, 0, 0, 1.,
-                         net::MEDIUM, false, false);
-  ResourceData font_resource =
-      CreateResourceData("http://www.resources.google.com/font.woff",
-                         content::RESOURCE_TYPE_FONT_RESOURCE, 11, 0, 0, 1.,
-                         net::MEDIUM, false, false);
-  float js_resource_score =
-      ResourcePrefetchPredictorTables::ComputeResourceScore(js_resource);
-  float css_resource_score =
-      ResourcePrefetchPredictorTables::ComputeResourceScore(css_resource);
-  float font_resource_score =
-      ResourcePrefetchPredictorTables::ComputeResourceScore(font_resource);
-  float image_resource_score =
-      ResourcePrefetchPredictorTables::ComputeResourceScore(image_resource);
-
-  EXPECT_TRUE(js_resource_score == css_resource_score);
-  EXPECT_TRUE(js_resource_score == font_resource_score);
-  EXPECT_NEAR(199., js_resource_score, 1e-4);
-  EXPECT_NEAR(99., image_resource_score, 1e-4);
+  auto compute_score = [](net::RequestPriority priority,
+                          content::ResourceType resource_type,
+                          double average_position) {
+    return ResourcePrefetchPredictorTables::ComputeResourceScore(
+        CreateResourceData("", resource_type, 0, 0, 0, average_position,
+                           priority, false, false));
+  };
+
+  // Priority is more important than the rest.
+  EXPECT_TRUE(compute_score(net::HIGHEST, content::RESOURCE_TYPE_SCRIPT, 1.) >
+              compute_score(net::HIGHEST, content::RESOURCE_TYPE_IMAGE, 42.));
+
+  EXPECT_TRUE(compute_score(net::HIGHEST, content::RESOURCE_TYPE_IMAGE, 42.) >
+              compute_score(net::MEDIUM, content::RESOURCE_TYPE_SCRIPT, 1.));
+  EXPECT_TRUE(compute_score(net::HIGHEST, content::RESOURCE_TYPE_IMAGE, 42.) >
+              compute_score(net::LOW, content::RESOURCE_TYPE_SCRIPT, 1.));
+  EXPECT_TRUE(compute_score(net::HIGHEST, content::RESOURCE_TYPE_IMAGE, 42.) >
+              compute_score(net::LOWEST, content::RESOURCE_TYPE_SCRIPT, 1.));
+  EXPECT_TRUE(compute_score(net::HIGHEST, content::RESOURCE_TYPE_IMAGE, 42.) >
+              compute_score(net::IDLE, content::RESOURCE_TYPE_SCRIPT, 1.));
+
+  // Scripts and stylesheets are equivalent.
+  EXPECT_NEAR(
+      compute_score(net::HIGHEST, content::RESOURCE_TYPE_SCRIPT, 42.),
+      compute_score(net::HIGHEST, content::RESOURCE_TYPE_STYLESHEET, 42.),
+      1e-4);
+
+  // Scripts are more important than fonts and images, and the rest.
+  EXPECT_TRUE(
+      compute_score(net::HIGHEST, content::RESOURCE_TYPE_SCRIPT, 42.) >
+      compute_score(net::HIGHEST, content::RESOURCE_TYPE_FONT_RESOURCE, 42.));
+  EXPECT_TRUE(
+      compute_score(net::HIGHEST, content::RESOURCE_TYPE_FONT_RESOURCE, 42.) >
+      compute_score(net::HIGHEST, content::RESOURCE_TYPE_IMAGE, 42.));
+  EXPECT_TRUE(
+      compute_score(net::HIGHEST, content::RESOURCE_TYPE_FONT_RESOURCE, 42.) >
+      compute_score(net::HIGHEST, content::RESOURCE_TYPE_FAVICON, 42.));
+
+  // All else being equal, position matters.
+  EXPECT_TRUE(compute_score(net::HIGHEST, content::RESOURCE_TYPE_SCRIPT, 12.) >
+              compute_score(net::HIGHEST, content::RESOURCE_TYPE_SCRIPT, 42.));
 }
 
 TEST_F(ResourcePrefetchPredictorTablesTest, GetAllData) {

tools/resource_prefetch_predictor/prefetch_predictor_tool.py

@@ -31,13 +31,23 @@ class Entry(object):
     self.score = self._Score()
 
   def _Score(self):
-    """Mirrors ResourcePrefetchPredictorTables::ResourceRow::UpdateScore."""
-    multiplier = 1
+    """Mirrors ResourcePrefetchPredictorTables::ComputeResourceScore."""
+    priority_multiplier = 1
+    type_multiplier = 1
+
+    if self.proto.priority == ResourceData.REQUEST_PRIORITY_HIGHEST:
+      priority_multiplier = 3
+    elif self.proto.priority == ResourceData.REQUEST_PRIORITY_MEDIUM:
+      priority_multiplier = 2
+
     if self.proto.resource_type in (ResourceData.RESOURCE_TYPE_STYLESHEET,
-                                    ResourceData.RESOURCE_TYPE_SCRIPT,
-                                    ResourceData.RESOURCE_TYPE_FONT_RESOURCE):
-      multiplier = 2
-    return multiplier * 100 - self.proto.average_position
+                                    ResourceData.RESOURCE_TYPE_SCRIPT):
+      type_multiplier = 3
+    elif self.proto.resource_type == ResourceData.RESOURCE_TYPE_FONT_RESOURCE:
+      type_multiplier = 2
+
+      return (100 * (priority_multiplier * 100 + type_multiplier * 10)
+              - self.proto.average_position)
 
   @classmethod
   def FromRow(cls, row):