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

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

Index: third_party/WebKit/Source/core/css/RemoteFontFaceSource.cpp
diff --git a/third_party/WebKit/Source/core/css/RemoteFontFaceSource.cpp b/third_party/WebKit/Source/core/css/RemoteFontFaceSource.cpp
index 638504edc43eb4d7de3a6f295989eb95929a4d1c..197c0999381f8ff83fd041380cb77989944de20c 100644
--- a/third_party/WebKit/Source/core/css/RemoteFontFaceSource.cpp
+++ b/third_party/WebKit/Source/core/css/RemoteFontFaceSource.cpp
@@ -218,6 +218,10 @@ 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();
 
@@ -275,6 +279,7 @@ void RemoteFontFaceSource::FontLoadHistograms::recordRemoteFont(const FontResour
     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);