[blink] Record FontDisplay enum using //base/metrics helpers.

This also converts FontDisplay to be a scoped enum, which allows:
- clang to enforce kMaxValue correctness
- autodeduction of the max value by UMA_HISTOGRAM_ENUMERATION.

Bug: 742517, 1047547
Change-Id: Iabb56121750acac4147e20bffe132bde190d9f7a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2505676
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Auto-Submit: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821901}

third_party/blink/renderer/core/css/font_display.cc

@@ -12,20 +12,20 @@ FontDisplay CSSValueToFontDisplay(const CSSValue* value) {
   if (auto* identifier_value = DynamicTo<CSSIdentifierValue>(value)) {
     switch (identifier_value->GetValueID()) {
       case CSSValueID::kAuto:
-        return kFontDisplayAuto;
+        return FontDisplay::kAuto;
       case CSSValueID::kBlock:
-        return kFontDisplayBlock;
+        return FontDisplay::kBlock;
       case CSSValueID::kSwap:
-        return kFontDisplaySwap;
+        return FontDisplay::kSwap;
       case CSSValueID::kFallback:
-        return kFontDisplayFallback;
+        return FontDisplay::kFallback;
       case CSSValueID::kOptional:
-        return kFontDisplayOptional;
+        return FontDisplay::kOptional;
       default:
         break;
     }
   }
-  return kFontDisplayAuto;
+  return FontDisplay::kAuto;
 }
 
 }  // namespace blink

third_party/blink/renderer/core/css/font_display.h

@@ -9,13 +9,15 @@ namespace blink {
 
 class CSSValue;
 
-enum FontDisplay {
-  kFontDisplayAuto,
-  kFontDisplayBlock,
-  kFontDisplaySwap,
-  kFontDisplayFallback,
-  kFontDisplayOptional,
-  kFontDisplayEnumMax,
+// These values are persisted to logs. Entries should not be renumbered and
+// numeric values should never be reused.
+enum class FontDisplay {
+  kAuto,
+  kBlock,
+  kSwap,
+  kFallback,
+  kOptional,
+  kMaxValue = kOptional,
 };
 
 FontDisplay CSSValueToFontDisplay(const CSSValue*);

third_party/blink/renderer/core/css/font_face.cc

@@ -30,6 +30,7 @@
 
 #include "third_party/blink/renderer/core/css/font_face.h"
 
+#include "base/metrics/histogram_macros.h"
 #include "third_party/blink/public/platform/task_type.h"
 #include "third_party/blink/renderer/bindings/core/v8/string_or_array_buffer_or_array_buffer_view.h"
 #include "third_party/blink/renderer/bindings/core/v8/v8_font_face_descriptors.h"
@@ -65,7 +66,6 @@
 #include "third_party/blink/renderer/platform/font_family_names.h"
 #include "third_party/blink/renderer/platform/fonts/font_metrics_override.h"
 #include "third_party/blink/renderer/platform/heap/heap.h"
-#include "third_party/blink/renderer/platform/instrumentation/histogram.h"
 #include "third_party/blink/renderer/platform/instrumentation/use_counter.h"
 #include "third_party/blink/renderer/platform/runtime_enabled_features.h"
 #include "third_party/blink/renderer/platform/wtf/shared_buffer.h"
@@ -836,10 +836,8 @@ void FontFace::InitCSSFontFace(ExecutionContext* context, const CSSValue& src) {
   }
 
   if (display_) {
-    DEFINE_THREAD_SAFE_STATIC_LOCAL(
-        EnumerationHistogram, font_display_histogram,
-        ("WebFont.FontDisplayValue", kFontDisplayEnumMax));
-    font_display_histogram.Count(CSSValueToFontDisplay(display_.Get()));
+    UMA_HISTOGRAM_ENUMERATION("WebFont.FontDisplayValue",
+                              CSSValueToFontDisplay(display_.Get()));
   }
 }
 

third_party/blink/renderer/core/css/remote_font_face_source.cc

@@ -31,7 +31,7 @@
 namespace blink {
 
 bool RemoteFontFaceSource::NeedsInterventionToAlignWithLCPGoal() const {
-  DCHECK_EQ(display_, kFontDisplayAuto);
+  DCHECK_EQ(display_, FontDisplay::kAuto);
   if (!base::FeatureList::IsEnabled(
           features::kAlignFontDisplayAutoTimeoutWithLCPGoal)) {
     return false;
@@ -51,7 +51,7 @@ bool RemoteFontFaceSource::NeedsInterventionToAlignWithLCPGoal() const {
 
 RemoteFontFaceSource::DisplayPeriod
 RemoteFontFaceSource::ComputeFontDisplayAutoPeriod() const {
-  DCHECK_EQ(display_, kFontDisplayAuto);
+  DCHECK_EQ(display_, FontDisplay::kAuto);
   if (NeedsInterventionToAlignWithLCPGoal()) {
     using Mode = features::AlignFontDisplayAutoTimeoutWithLCPGoalMode;
     Mode mode =
@@ -79,9 +79,9 @@ RemoteFontFaceSource::ComputeFontDisplayAutoPeriod() const {
 RemoteFontFaceSource::DisplayPeriod RemoteFontFaceSource::ComputePeriod()
     const {
   switch (display_) {
-    case kFontDisplayAuto:
+    case FontDisplay::kAuto:
       return ComputeFontDisplayAutoPeriod();
-    case kFontDisplayBlock:
+    case FontDisplay::kBlock:
       switch (phase_) {
         case kNoLimitExceeded:
         case kShortLimitExceeded:
@@ -90,10 +90,10 @@ RemoteFontFaceSource::DisplayPeriod RemoteFontFaceSource::ComputePeriod()
           return kSwapPeriod;
       }
 
-    case kFontDisplaySwap:
+    case FontDisplay::kSwap:
       return kSwapPeriod;
 
-    case kFontDisplayFallback:
+    case FontDisplay::kFallback:
       switch (phase_) {
         case kNoLimitExceeded:
           return kBlockPeriod;
@@ -103,7 +103,7 @@ RemoteFontFaceSource::DisplayPeriod RemoteFontFaceSource::ComputePeriod()
           return kFailurePeriod;
       }
 
-    case kFontDisplayOptional: {
+    case FontDisplay::kOptional: {
       const bool use_phase_value =
           !base::FeatureList::IsEnabled(
               features::kFontPreloadingDelaysRendering) ||
@@ -132,9 +132,6 @@ RemoteFontFaceSource::DisplayPeriod RemoteFontFaceSource::ComputePeriod()
 
       return kSwapPeriod;
     }
-    case kFontDisplayEnumMax:
-      NOTREACHED();
-      break;
   }
   NOTREACHED();
   return kSwapPeriod;
@@ -295,11 +292,11 @@ FontDisplay RemoteFontFaceSource::GetFontDisplayWithDocumentPolicyCheck(
     const FontSelector* font_selector,
     ReportOptions report_option) const {
   ExecutionContext* context = font_selector->GetExecutionContext();
-  if (display != kFontDisplayFallback && display != kFontDisplayOptional &&
+  if (display != FontDisplay::kFallback && display != FontDisplay::kOptional &&
       context && context->IsWindow() &&
       !context->IsFeatureEnabled(
           mojom::blink::DocumentPolicyFeature::kFontDisplay, report_option)) {
-    return kFontDisplayOptional;
+    return FontDisplay::kOptional;
   }
   return display;
 }
@@ -315,7 +312,7 @@ bool RemoteFontFaceSource::ShouldTriggerWebFontsIntervention() {
       WebEffectiveConnectionType::kTypeOffline <= connection_type &&
       connection_type <= WebEffectiveConnectionType::kType3G;
 
-  return network_is_slow && display_ == kFontDisplayAuto;
+  return network_is_slow && display_ == FontDisplay::kAuto;
 }
 
 bool RemoteFontFaceSource::IsLowPriorityLoadingAllowedForRemoteFont() const {