Revert of Make the HTMLDocumentParser yield more aggressively

Source/core/html/parser/HTMLDocumentParser.cpp

Index: Source/core/html/parser/HTMLDocumentParser.cpp
diff --git a/Source/core/html/parser/HTMLDocumentParser.cpp b/Source/core/html/parser/HTMLDocumentParser.cpp
index 3a5c940aacbb84c63fd477645c69517bc5a0a320..9f9c44dbbffa480ec5f94314793f8f0bfcdf0140 100644
--- a/Source/core/html/parser/HTMLDocumentParser.cpp
+++ b/Source/core/html/parser/HTMLDocumentParser.cpp
@@ -317,31 +317,25 @@
 {
     TRACE_EVENT0("blink", "HTMLDocumentParser::didReceiveParsedChunkFromBackgroundParser");
 
-    if (!isParsing())
-        return;
-
-    // ApplicationCache needs to be initialized before issuing preloads.
-    // We suspend preload until HTMLHTMLElement is inserted and
-    // ApplicationCache is initialized.
-    if (!document()->documentElement()) {
-        for (auto& request : chunk->preloads)
-            m_queuedPreloads.append(request.release());
-    } else {
-        // We can safely assume that there are no queued preloads request after
-        // the document element is available, as we empty the queue immediately
-        // after the document element is created in pumpPendingSpeculations().
-        ASSERT(m_queuedPreloads.isEmpty());
-        m_preloader->takeAndPreload(chunk->preloads);
-    }
-
-    m_speculations.append(chunk);
-
-    if (!isWaitingForScripts() && !isScheduledForResume()) {
+    // alert(), runModalDialog, and the JavaScript Debugger all run nested event loops
+    // which can cause this method to be re-entered. We detect re-entry using
+    // hasActiveParser(), save the chunk as a speculation, and return.
+    if (isWaitingForScripts() || !m_speculations.isEmpty() || document()->activeParserCount() > 0 || m_tasksWereSuspended || isScheduledForResume()) {
         if (m_tasksWereSuspended)
             m_parserScheduler->forceResumeAfterYield();
-        else
-            m_parserScheduler->scheduleForResume();
-    }
+        m_preloader->takeAndPreload(chunk->preloads);
+        m_speculations.append(chunk);
+        return;
+    }
+
+    // processParsedChunkFromBackgroundParser can cause this parser to be detached from the Document,
+    // but we need to ensure it isn't deleted yet.
+    RefPtrWillBeRawPtr<HTMLDocumentParser> protect(this);
+
+    ASSERT(m_speculations.isEmpty());
+    chunk->preloads.clear(); // We don't need to preload because we're going to parse immediately.
+    m_speculations.append(chunk);
+    pumpPendingSpeculations();
 }
 
 void HTMLDocumentParser::didReceiveEncodingDataFromBackgroundParser(const DocumentEncodingData& data)
@@ -458,9 +452,6 @@
         m_textPosition = it->textPosition();
 
         constructTreeFromCompactHTMLToken(*it);
-
-        if (!m_queuedPreloads.isEmpty() && document()->documentElement())
-            m_preloader->takeAndPreload(m_queuedPreloads);
 
         if (isStopped())
             break;