FontLoadHistograms: classify as memory cache hit if FontResource loading not triggered

third_party/WebKit/Source/core/css/RemoteFontFaceSource.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/css/RemoteFontFaceSource.h"
 
 #include "core/css/CSSCustomFontData.h"
 #include "core/css/CSSFontFace.h"
 #include "core/css/CSSFontSelector.h"
 #include "core/dom/Document.h"
@@ skipping 253 matching lines @@
     if (m_blankPaintTime <= 0)
         return;
     int duration = static_cast<int>(currentTimeMS() - m_blankPaintTime);
     DEFINE_STATIC_LOCAL(CustomCountHistogram, blankTextShownTimeHistogram, ("WebFont.BlankTextShownTime", 0, 10000, 50));
     blankTextShownTimeHistogram.count(duration);
     m_blankPaintTime = -1;
 }
 
 void RemoteFontFaceSource::FontLoadHistograms::recordRemoteFont(const FontResource* font)
 {
+    if (m_dataSource == FromDiskCache || m_dataSource == FromNetwork) {
+        // Collect load time only if |m_loadStartTime| was set, i.e. the owning
+        // RemoteFontFaceSource instance started the loading of |m_font|.
+        // Otherwise we classify as memory cache hit.
+        if (m_loadStartTime) {
+            int duration = static_cast<int>(currentTimeMS() - m_loadStartTime);
+            recordLoadTimeHistogram(font, duration);
+
+            enum { CORSFail, CORSSuccess, CORSEnumMax };
+            int corsValue = font->isCORSFailed() ? CORSFail : CORSSuccess;
+            DEFINE_STATIC_LOCAL(EnumerationHistogram, corsHistogram, ("WebFont.CORSSuccess", CORSEnumMax));
+            corsHistogram.count(corsValue);
+        } else {
+            m_dataSource = FromMemoryCache;

[Kunihiko Sakamoto, 2016/09/23 07:39:18]

Before this patch, we only had transitions from FromUnknown to others. This
introduces a path from From{DiskCache,Network} to FromMemoryCache - I think this
makes it hard to reason about this field.

Instead, can we do this in the maySetDataSource() call at line 110?

[Shao-Chuan Lee, 2016/09/23 08:41:06]

Done.

+        }
+    }
+
     DEFINE_STATIC_LOCAL(EnumerationHistogram, cacheHitHistogram, ("WebFont.CacheHit", CacheHitEnumMax));
     cacheHitHistogram.count(dataSourceMetricsValue());
-
-    if (m_dataSource == FromDiskCache || m_dataSource == FromNetwork) {
-        int duration = static_cast<int>(currentTimeMS() - m_loadStartTime);
-        recordLoadTimeHistogram(font, duration);
-
-        enum { CORSFail, CORSSuccess, CORSEnumMax };
-        int corsValue = font->isCORSFailed() ? CORSFail : CORSSuccess;
-        DEFINE_STATIC_LOCAL(EnumerationHistogram, corsHistogram, ("WebFont.CORSSuccess", CORSEnumMax));
-        corsHistogram.count(corsValue);
-    }
 }
 
 void RemoteFontFaceSource::FontLoadHistograms::recordLoadTimeHistogram(const FontResource* font, int duration)
 {
     CHECK_NE(FromUnknown, m_dataSource);
 
     if (font->errorOccurred()) {
         DEFINE_STATIC_LOCAL(CustomCountHistogram, loadErrorHistogram, ("WebFont.DownloadTime.LoadError", 0, 10000, 50));
         DEFINE_STATIC_LOCAL(CustomCountHistogram, missedCacheLoadErrorHistogram, ("WebFont.MissedCache.DownloadTime.LoadError", 0, 10000, 50));
         loadErrorHistogram.count(duration);
@@ skipping 74 matching lines @@
         return Miss;
     case FromUnknown:
         // Fall through.
     default:
         NOTREACHED();
     }
     return Miss;
 }
 
 } // namespace blink