diff --git a/third_party/WebKit/Source/core/html/parser/BackgroundHTMLParser.cpp b/third_party/WebKit/Source/core/html/parser/BackgroundHTMLParser.cpp
index 1fc0675bbef894..fc66a5b945cfcd 100644
--- a/third_party/WebKit/Source/core/html/parser/BackgroundHTMLParser.cpp
+++ b/third_party/WebKit/Source/core/html/parser/BackgroundHTMLParser.cpp
@@ -112,6 +112,7 @@ BackgroundHTMLParser::BackgroundHTMLParser(PassRefPtr<WeakReference<BackgroundHT
     , m_loadingTaskRunner(std::move(loadingTaskRunner))
     , m_parsedChunkQueue(config->parsedChunkQueue.release())
     , m_startingScript(false)
+    , m_lastBytesReceivedTime(0.0)
 {
     ASSERT(m_outstandingTokenLimit > 0);
     ASSERT(m_pendingTokenLimit > 0);
@@ -122,15 +123,12 @@ BackgroundHTMLParser::~BackgroundHTMLParser()
 {
 }
 
-void BackgroundHTMLParser::appendRawBytesFromParserThread(const char* data, int dataLength)
-{
-    ASSERT(m_decoder);
-    updateDocument(m_decoder->decode(data, dataLength));
-}
-
-void BackgroundHTMLParser::appendRawBytesFromMainThread(std::unique_ptr<Vector<char>> buffer)
+void BackgroundHTMLParser::appendRawBytesFromMainThread(std::unique_ptr<Vector<char>> buffer, double bytesReceivedTime)
 {
     ASSERT(m_decoder);
+    m_lastBytesReceivedTime = bytesReceivedTime;
+    DEFINE_STATIC_LOCAL(CustomCountHistogram, queueDelay, ("Parser.AppendBytesDelay", 1, 5000, 50));
+    queueDelay.count(monotonicallyIncreasingTimeMS() - bytesReceivedTime);
     updateDocument(m_decoder->decode(buffer->data(), buffer->size()));
 }
 
@@ -180,6 +178,7 @@ void BackgroundHTMLParser::resumeFrom(std::unique_ptr<Checkpoint> checkpoint)
     m_preloadScanner->rewindTo(checkpoint->preloadScannerCheckpoint);
     m_startingScript = false;
     m_parsedChunkQueue->clear();
+    m_lastBytesReceivedTime = monotonicallyIncreasingTimeMS();
     pumpTokenizer();
 }
 
@@ -293,6 +292,12 @@ void BackgroundHTMLParser::sendTokensToMainThread()
     std::unique_ptr<HTMLDocumentParser::ParsedChunk> chunk = wrapUnique(new HTMLDocumentParser::ParsedChunk);
     TRACE_EVENT_WITH_FLOW0("blink,loading", "BackgroundHTMLParser::sendTokensToMainThread", chunk.get(), TRACE_EVENT_FLAG_FLOW_OUT);
 
+    if (!m_pendingPreloads.isEmpty()) {
+        double delay = monotonicallyIncreasingTimeMS() - m_lastBytesReceivedTime;
+        DEFINE_STATIC_LOCAL(CustomCountHistogram, preloadTokenizeDelay, ("Parser.PreloadTokenizeDelay", 1, 10000, 50));
+        preloadTokenizeDelay.count(delay);
+    }
+
     chunk->preloads.swap(m_pendingPreloads);
     if (m_viewportDescription.set)
         chunk->viewport = m_viewportDescription;
diff --git a/third_party/WebKit/Source/core/html/parser/BackgroundHTMLParser.h b/third_party/WebKit/Source/core/html/parser/BackgroundHTMLParser.h
index 3f2c4601807781..85564bb1daa4b9 100644
--- a/third_party/WebKit/Source/core/html/parser/BackgroundHTMLParser.h
+++ b/third_party/WebKit/Source/core/html/parser/BackgroundHTMLParser.h
@@ -78,9 +78,7 @@ class BackgroundHTMLParser {
         String unparsedInput;
     };
 
-    void appendRawBytesFromParserThread(const char* data, int dataLength);
-
-    void appendRawBytesFromMainThread(std::unique_ptr<Vector<char>>);
+    void appendRawBytesFromMainThread(std::unique_ptr<Vector<char>>, double bytesReceivedTime);
     void setDecoder(std::unique_ptr<TextResourceDecoder>);
     void flush();
     void resumeFrom(std::unique_ptr<Checkpoint>);
@@ -128,6 +126,7 @@ class BackgroundHTMLParser {
     RefPtr<ParsedChunkQueue> m_parsedChunkQueue;
 
     bool m_startingScript;
+    double m_lastBytesReceivedTime;
 };
 
 } // namespace blink
diff --git a/third_party/WebKit/Source/core/html/parser/HTMLDocumentParser.cpp b/third_party/WebKit/Source/core/html/parser/HTMLDocumentParser.cpp
index eee5367bedca27..ae3ed16a83cceb 100644
--- a/third_party/WebKit/Source/core/html/parser/HTMLDocumentParser.cpp
+++ b/third_party/WebKit/Source/core/html/parser/HTMLDocumentParser.cpp
@@ -1024,6 +1024,7 @@ void HTMLDocumentParser::appendBytes(const char* data, size_t length)
         return;
 
     if (shouldUseThreading()) {
+        double bytesReceivedTime = monotonicallyIncreasingTimeMS();
         if (!m_haveBackgroundParser)
             startBackgroundParser();
 
@@ -1031,7 +1032,7 @@ void HTMLDocumentParser::appendBytes(const char* data, size_t length)
         memcpy(buffer->data(), data, length);
         TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("blink.debug"), "HTMLDocumentParser::appendBytes", "size", (unsigned)length);
 
-        postTaskToLookaheadParser(threadSafeBind(&BackgroundHTMLParser::appendRawBytesFromMainThread, m_backgroundParser, passed(std::move(buffer))));
+        postTaskToLookaheadParser(threadSafeBind(&BackgroundHTMLParser::appendRawBytesFromMainThread, m_backgroundParser, passed(std::move(buffer)), bytesReceivedTime));
         return;
     }
 
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 5ef2c93c7e9cb4..ce58180faf88c4 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -37423,6 +37423,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Parser.AppendBytesDelay" units="ms">
+  <owner>csharrison@chromium.org</owner>
+  <summary>
+    The delay from when bytes are received on the main thread to when the
+    BackgroundHTMLParser starts tokenizing them. Always a shorter time than the
+    time emitted to Parser.PreloadTokenizeDelay.
+  </summary>
+</histogram>
+
 <histogram name="Parser.ChunkEnqueueTime" units="ms">
   <owner>csharrison@chromium.org</owner>
   <summary>
@@ -37454,6 +37463,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Parser.PreloadTokenizeDelay" units="ms">
+  <owner>csharrison@chromium.org</owner>
+  <summary>
+    The delay from when bytes are received on the main thread to when they are
+    tokenized and preloads are sent back to the main parser. Always a greater
+    time than the time emitted to Parser.AppendBytesDelay.
+  </summary>
+</histogram>
+
 <histogram name="PartitionAlloc.CommittedSize" units="MB">
   <owner>haraken@chromium.org</owner>
   <summary>