Add UMA in preparation of running the ParserMainThread experiment

This patch adds the following metrics:
- queueing delay from bytes received on the main thread to bytes received
on the BackgroundHTMLParser
- preload delay measured from bytes received on the main thread to preloads
sent to the main thread

The patch also gets rid of the appendRawBytesFromParserThread method,
which was dead code.

BUG=623165,603274

Review-Url: https://codereview.chromium.org/2097973002
Cr-Commit-Position: refs/heads/master@{#402516}

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;

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

third_party/WebKit/Source/core/html/parser/HTMLDocumentParser.cpp

@@ -1024,14 +1024,15 @@ void HTMLDocumentParser::appendBytes(const char* data, size_t length)
         return;
 
     if (shouldUseThreading()) {
+        double bytesReceivedTime = monotonicallyIncreasingTimeMS();
         if (!m_haveBackgroundParser)
             startBackgroundParser();
 
         std::unique_ptr<Vector<char>> buffer = wrapUnique(new Vector<char>(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;
     }
 

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>[email protected]</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>[email protected]</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>[email protected]</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>[email protected]</owner>
   <summary>