Set WebFont priority to very low if the network is detected to be slow

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"
 #include "core/fetch/ResourceFetcher.h"
 #include "core/inspector/ConsoleMessage.h"
 #include "core/loader/FrameLoaderClient.h"
 #include "core/page/NetworkStateNotifier.h"
 #include "platform/Histogram.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/fonts/FontCache.h"
 #include "platform/fonts/FontDescription.h"
 #include "platform/fonts/SimpleFontData.h"
+#include "platform/network/ResourceLoadPriority.h"
 #include "public/platform/WebEffectiveConnectionType.h"
 #include "wtf/CurrentTime.h"
 
 namespace blink {
 
 namespace {
 
 bool isEffectiveConnectionTypeSlowFor(Document* document) {
   WebEffectiveConnectionType type =
       document->frame()->loader().client()->getEffectiveConnectionType();
@@ skipping 163 matching lines @@
       RuntimeEnabledFeatures::webFontsInterventionV2With3GEnabled() ||
       RuntimeEnabledFeatures::webFontsInterventionV2WithSlow2GEnabled();
 
   bool networkIsSlow =
       isV2Enabled ? isEffectiveConnectionTypeSlowFor(m_fontSelector->document())
                   : isConnectionTypeSlow();
 
   return networkIsSlow && m_display == FontDisplayAuto;
 }
 
+bool RemoteFontFaceSource::isLowPriorityLoadingAllowedForRemoteFont() const {
+  return m_isInterventionTriggered;
+}
+
 PassRefPtr<SimpleFontData> RemoteFontFaceSource::createFontData(
     const FontDescription& fontDescription) {
   if (!isLoaded())
     return createLoadingFallbackFontData(fontDescription);
 
   if (!m_font->ensureCustomFontData() || m_period == FailurePeriod)
     return nullptr;
 
   m_histograms.recordFallbackTime(m_font.get());
 
@@ skipping 17 matching lines @@
     return nullptr;
   }
   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()) {
+    if (!m_font->url().protocolIsData() && !m_font->isLoaded() &&
+        m_display == FontDisplayAuto &&
+        m_font->isLowPriorityLoadingAllowedForRemoteFont()) {
+      // Set the loading priority to VeryLow since this font is not required
+      // for painting the text.
+      m_font->didChangePriority(ResourceLoadPriorityVeryLow, 0);
+    }
     m_fontSelector->document()->fetcher()->startLoad(m_font);
     if (!m_font->isLoaded())
       m_font->startLoadLimitTimers();
     m_histograms.loadStarted();
   }
 
   if (m_face)
     m_face->didBeginLoad();
 }
 
@@ skipping 202 matching lines @@
       return Miss;
     case FromUnknown:
     // Fall through.
     default:
       NOTREACHED();
   }
   return Miss;
 }
 
 }  // namespace blink