Make it possible to modify background HTML parser token limits.

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 5fa1975ebf40a4a712dd6115436d7b06cfd5caf2..9d974e0a017e013946ed96b271fb4262b5c6c1b2 100644
--- a/Source/core/html/parser/HTMLDocumentParser.cpp
+++ b/Source/core/html/parser/HTMLDocumentParser.cpp
@@ -783,6 +783,12 @@ void HTMLDocumentParser::startBackgroundParser()
     config->xssAuditor->init(document(), &m_xssAuditorDelegate);
     config->preloadScanner = adoptPtr(new TokenPreloadScanner(document()->url().copy(), CachedDocumentParameters::create(document())));
     config->decoder = takeDecoder();
+    if (document()->settings()) {

[Nate Chapin, 2015/06/11 18:48:23]

I think Document::settings should only be null here for XHR document responses.
Any thoughts on whether it's a bad thing to use the defaults for those kinds of
document?

[Bryan McQuade, 2015/06/12 14:12:59]

Ah, interesting. I think varying these constants are less important for XHR'd
documents. The primary motivation for being able to change these values is to be
able to control how much we look ahead of the parser with the preload scanner,
which isn't relevant for XHR'd documents - IIUC XHR'd docs don't actually
trigger fetches for things like <scripts> until they are inserted into an HTML
document(let me know if that's not right). So I think this is ok. Let me know if
you disagree though.

[Nate Chapin, 2015/06/12 17:02:59]

I'm not terribly familiar with our XHR document logic, but in general I agree
that documents without a frame() shouldn't be able to request subresources.

+        if (document()->settings()->backgroundHtmlParserOutstandingTokenLimit() > 0)
+            config->outstandingTokenLimit = document()->settings()->backgroundHtmlParserOutstandingTokenLimit();
+        if (document()->settings()->backgroundHtmlParserPendingTokenLimit() > 0)

[Nate Chapin, 2015/06/11 18:48:23]

if these become unsigned, drop the " > 0"

[Bryan McQuade, 2015/06/12 14:12:59]

Done.

+            config->pendingTokenLimit = document()->settings()->backgroundHtmlParserPendingTokenLimit();
+    }
 
     ASSERT(config->xssAuditor->isSafeToSendToAnotherThread());
     ASSERT(config->preloadScanner->isSafeToSendToAnotherThread());