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 200 matching lines @@
     }
     RefPtr<CSSCustomFontData> cssFontData = CSSCustomFontData::create(this, m_period == BlockPeriod ? CSSCustomFontData::InvisibleFallback : CSSCustomFontData::VisibleFallback);
     return SimpleFontData::create(temporaryFont->platformData(), cssFontData);
 }
 
 void RemoteFontFaceSource::beginLoadIfNeeded()
 {
     if (m_fontSelector->document() && m_font->stillNeedsLoad()) {
         m_fontSelector->document()->fetcher()->startLoad(m_font);
         m_histograms.loadStarted();
+    } else {
+        // In this case the |m_font| loading is already started by another
+        // RemoteFontFaceSource instance, classify as memory cache hit.
+        m_histograms.maySetDataSource(FontLoadHistograms::FromMemoryCache);
     }
     m_font->startLoadLimitTimersIfNeeded();
 
     if (m_face)
         m_face->didBeginLoad();
 }
 
 DEFINE_TRACE(RemoteFontFaceSource)
 {
     visitor->trace(m_font);
@@ skipping 37 matching lines @@
     blankTextShownTimeHistogram.count(duration);
     m_blankPaintTime = -1;
 }
 
 void RemoteFontFaceSource::FontLoadHistograms::recordRemoteFont(const FontResource* font)
 {
     DEFINE_STATIC_LOCAL(EnumerationHistogram, cacheHitHistogram, ("WebFont.CacheHit", CacheHitEnumMax));
     cacheHitHistogram.count(dataSourceMetricsValue());
 
     if (m_dataSource == FromDiskCache || m_dataSource == FromNetwork) {
+        DCHECK(m_loadStartTime);

[kouhei (in TOK), 2016/09/23 01:33:59]

using DCHECK on double scares me a bit.
DCHECK_LT(m_loadStartTime, 0.0); perhaps?

[Shao-Chuan Lee, 2016/09/23 01:47:19]

Checking if non-zero should suffice here, maybe I should use
DCHECK_NE(m_loadStartTime, 0) to be clear?

[kouhei (in TOK), 2016/09/30 01:18:35]

DCHECK_NE(m_loadStartTime, 0.0) is also OK.

         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);
     }
 }
 
@@ skipping 82 matching lines @@
         return Miss;
     case FromUnknown:
         // Fall through.
     default:
         NOTREACHED();
     }
     return Miss;
 }
 
 } // namespace blink