Use array to represent internal feature state of document policy

Previously, document policy class is designed to hold a field for each
feature's policy value. Those fields are supposed to be generated from
document_policy_features.json5. Such design minimizes both speed and
memory overhead but adds complexity to the system by introducing code
generation.

This CL uses array to represent internal feature state, which still
minimizes speed overhead as indexing into array is the same as indexing
into memory, and adds very little memory overhead(Each PolicyValue
instance contains extra information).

Change-Id: I4bc5e9b4383c628018e2605ad896e31b17c9c0e9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2003436
Commit-Queue: Charlie Hu <chenleihu@google.com>
Reviewed-by: Ian Clelland <iclelland@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732682}

third_party/blink/common/feature_policy/document_policy.cc

@@ -226,17 +226,8 @@ DocumentPolicy::FeatureState DocumentPolicy::MergeFeatureState(
 bool DocumentPolicy::IsFeatureEnabled(
     mojom::FeaturePolicyFeature feature) const {
   mojom::PolicyValueType feature_type = GetFeatureDefaults().at(feature).Type();
-  // TODO(iclelland): Generate this switch block
-  switch (feature) {
-    case mojom::FeaturePolicyFeature::kFontDisplay:
-      return font_display_;
-    case mojom::FeaturePolicyFeature::kUnoptimizedLosslessImages:
-      return PolicyValue(unoptimized_lossless_images_) >=
-             PolicyValue::CreateMaxPolicyValue(feature_type);
-    default:
-      NOTREACHED();
-      return true;
-  }
+  return IsFeatureEnabled(feature,
+                          PolicyValue::CreateMaxPolicyValue(feature_type));
 }
 
 bool DocumentPolicy::IsFeatureEnabled(
@@ -247,16 +238,7 @@ bool DocumentPolicy::IsFeatureEnabled(
 
 PolicyValue DocumentPolicy::GetFeatureValue(
     mojom::FeaturePolicyFeature feature) const {
-  // TODO(iclelland): Generate this switch block
-  switch (feature) {
-    case mojom::FeaturePolicyFeature::kFontDisplay:
-      return PolicyValue(font_display_);
-    case mojom::FeaturePolicyFeature::kUnoptimizedLosslessImages:
-      return PolicyValue(unoptimized_lossless_images_);
-    default:
-      NOTREACHED();
-      return PolicyValue(false);
-  }
+  return internal_feature_state_[static_cast<size_t>(feature)];
 }
 
 bool DocumentPolicy::IsFeatureSupported(
@@ -273,30 +255,11 @@ bool DocumentPolicy::IsFeatureSupported(
 
 void DocumentPolicy::UpdateFeatureState(const FeatureState& feature_state) {
   for (const auto& feature_and_value : feature_state) {
-    // TODO(iclelland): Generate this switch block
-    switch (feature_and_value.first) {
-      case mojom::FeaturePolicyFeature::kFontDisplay:
-        font_display_ = feature_and_value.second.BoolValue();
-        break;
-      case mojom::FeaturePolicyFeature::kUnoptimizedLosslessImages:
-        unoptimized_lossless_images_ = feature_and_value.second.DoubleValue();
-        break;
-      default:
-        NOTREACHED();
-    }
+    internal_feature_state_[static_cast<size_t>(feature_and_value.first)] =
+        feature_and_value.second;
   }
 }
 
-DocumentPolicy::FeatureState DocumentPolicy::GetFeatureState() const {
-  FeatureState feature_state;
-  // TODO(iclelland): Generate this block
-  feature_state[mojom::FeaturePolicyFeature::kFontDisplay] =
-      PolicyValue(font_display_);
-  feature_state[mojom::FeaturePolicyFeature::kUnoptimizedLosslessImages] =
-      PolicyValue(unoptimized_lossless_images_);
-  return feature_state;
-}
-
 DocumentPolicy::DocumentPolicy(const FeatureState& defaults) {
   UpdateFeatureState(defaults);
 }

third_party/blink/public/common/feature_policy/document_policy.h

@@ -13,7 +13,7 @@
 #include "base/macros.h"
 #include "third_party/blink/public/common/common_export.h"
 #include "third_party/blink/public/common/feature_policy/policy_value.h"
-#include "third_party/blink/public/mojom/feature_policy/feature_policy_feature.mojom-forward.h"
+#include "third_party/blink/public/mojom/feature_policy/feature_policy_feature.mojom.h"
 #include "third_party/blink/public/mojom/feature_policy/policy_value.mojom.h"
 
 namespace blink {
@@ -88,11 +88,6 @@ class BLINK_COMMON_EXPORT DocumentPolicy {
   // Returns the value of the given feature on the given origin.
   PolicyValue GetFeatureValue(mojom::FeaturePolicyFeature feature) const;
 
-  // Returns the current threshold values assigned to all document policies.
-  // the declared header policy as well as any unadvertised required policies
-  // (such as sandbox policies).
-  FeatureState GetFeatureState() const;
-
   // Returns true if the incoming policy is compatible with the given required
   // policy, i.e. incoming policy is at least as strict as required policy.
   static bool IsPolicyCompatible(const FeatureState& required_policy,
@@ -124,11 +119,10 @@ class BLINK_COMMON_EXPORT DocumentPolicy {
 
   void UpdateFeatureState(const FeatureState& feature_state);
 
-  // Threshold values for each defined feature.
-  // TODO(iclelland): Generate these members; pack booleans in bitfields if
-  // possible.
-  bool font_display_ = true;
-  double unoptimized_lossless_images_ = std::numeric_limits<double>::infinity();
+  // Internal feature state is represented as an array to avoid overhead
+  // in using container classes.
+  PolicyValue internal_feature_state_
+      [static_cast<size_t>(mojom::FeaturePolicyFeature::kMaxValue) + 1];
 
   DISALLOW_COPY_AND_ASSIGN(DocumentPolicy);
 };