Add HTML parser UMA for rewinds and chunk queue statistics.

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

Index: third_party/WebKit/Source/core/html/parser/HTMLDocumentParser.cpp
diff --git a/third_party/WebKit/Source/core/html/parser/HTMLDocumentParser.cpp b/third_party/WebKit/Source/core/html/parser/HTMLDocumentParser.cpp
index 69f8d510dc4e3d0fa584237ed3c124a2acd1ed92..a46ddb3b6203a20acab153954d2942053d354031 100644
--- a/third_party/WebKit/Source/core/html/parser/HTMLDocumentParser.cpp
+++ b/third_party/WebKit/Source/core/html/parser/HTMLDocumentParser.cpp
@@ -156,6 +156,13 @@ DEFINE_TRACE(HTMLDocumentParser)
 
 void HTMLDocumentParser::detach()
 {
+    if (!isParsingFragment() && m_parsedChunkQueue.get() && m_parsedChunkQueue->peakPendingChunkCount()) {
+        DEFINE_STATIC_LOCAL(CustomCountHistogram, peakPendingChunkHistogram, ("Parser.PeakPendingChunkCount", 1, 1000, 50));
+        peakPendingChunkHistogram.count(m_parsedChunkQueue->peakPendingChunkCount());
+        DEFINE_STATIC_LOCAL(CustomCountHistogram, peakPendingTokenHistogram, ("Parser.PeakPendingTokenCount", 1, 100000, 50));
+        peakPendingTokenHistogram.count(m_parsedChunkQueue->peakPendingTokenCount());
+    }
+
     if (m_haveBackgroundParser)
         stopBackgroundParser();
     DocumentParser::detach();
@@ -382,7 +389,16 @@ void HTMLDocumentParser::validateSpeculations(PassOwnPtr<ParsedChunk> chunk)
 
 void HTMLDocumentParser::discardSpeculationsAndResumeFrom(PassOwnPtr<ParsedChunk> lastChunkBeforeScript, PassOwnPtr<HTMLToken> token, PassOwnPtr<HTMLTokenizer> tokenizer)
 {
+    TRACE_EVENT0("blink,loading", "HTMLDocumentParser::discardSpeculationsAndResumeFrom");

[kouhei (in TOK), 2016/06/17 11:20:57]

caseq: Would you review this TRACE_EVENT?

     m_weakFactory.revokeAll();
+
+    size_t discardedTokenCount = 0;
+    for (const auto& speculation : m_speculations) {
+        discardedTokenCount += speculation->tokens->size();
+    }
+    DEFINE_STATIC_LOCAL(CustomCountHistogram, discardedTokenCountHistogram, ("Parser.DiscardedTokenCount", 1, 100000, 50));
+    discardedTokenCountHistogram.count(discardedTokenCount);
+
     m_speculations.clear();
 
     OwnPtr<BackgroundHTMLParser::Checkpoint> checkpoint = adoptPtr(new BackgroundHTMLParser::Checkpoint);