Fix LinkStyle SRI check when against 0 sized resource.

third_party/WebKit/Source/core/html/HTMLLinkElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights
  * reserved.
  * Copyright (C) 2009 Rob Buis (rwlbuis@gmail.com)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 416 matching lines @@
   }
 
   // See the comment in PendingScript.cpp about why this check is necessary
   // here, instead of in the resource fetcher. https://crbug.com/500701.
   if (!cachedStyleSheet->errorOccurred() &&
       !m_owner->fastGetAttribute(HTMLNames::integrityAttr).isEmpty() &&
       !cachedStyleSheet->integrityMetadata().isEmpty()) {
     ResourceIntegrityDisposition disposition =
         cachedStyleSheet->integrityDisposition();
 
-    DCHECK(disposition != ResourceIntegrityDisposition::NotChecked ||
-           !cachedStyleSheet->sheetText().isNull());
-
     if (disposition == ResourceIntegrityDisposition::NotChecked &&
         !cachedStyleSheet->loadFailedOrCanceled()) {
-      DCHECK(cachedStyleSheet->resourceBuffer());
-      if (SubresourceIntegrity::CheckSubresourceIntegrity(
-              *m_owner, cachedStyleSheet->resourceBuffer()->data(),
-              cachedStyleSheet->resourceBuffer()->size(), KURL(baseURL, href),
-              *cachedStyleSheet))
-        disposition = ResourceIntegrityDisposition::Passed;
-      else
-        disposition = ResourceIntegrityDisposition::Failed;
+      bool checkResult;
+      if (cachedStyleSheet->resourceBuffer()) {

[jww, 2016/10/14 17:42:11]

nit: This could be simplified by having a const char* data and size_t size
variables that are set based on if there is a resourceBuffer or not, and then
having one call to SubresourceIntegrity::CheckSubresourceIntegrity().

Definitely a style preference, though, so whatever you prefer.

[kouhei (in TOK), 2016/10/17 01:23:38]

Done.

+        checkResult = SubresourceIntegrity::CheckSubresourceIntegrity(
+            *m_owner, cachedStyleSheet->resourceBuffer()->data(),
+            cachedStyleSheet->resourceBuffer()->size(), KURL(baseURL, href),
+            *cachedStyleSheet);
+      } else {
+        // If resourceBuffer is nullptr, the resource content-size was 0.
+        checkResult = SubresourceIntegrity::CheckSubresourceIntegrity(
+            *m_owner, nullptr, 0, KURL(baseURL, href), *cachedStyleSheet);
+      }
+      disposition = checkResult ? ResourceIntegrityDisposition::Passed
+                                : ResourceIntegrityDisposition::Failed;
 
       // TODO(kouhei): Remove this const_cast crbug.com/653502
       const_cast<CSSStyleSheetResource*>(cachedStyleSheet)
           ->setIntegrityDisposition(disposition);
     }
 
     if (disposition == ResourceIntegrityDisposition::Failed) {
       m_loading = false;
       removePendingSheet();
       notifyLoadedSheetAndAllCriticalSubresources(
@@ skipping 302 matching lines @@
     removePendingSheet();
 }
 
 DEFINE_TRACE(LinkStyle) {
   visitor->trace(m_sheet);
   LinkResource::trace(visitor);
   ResourceOwner<StyleSheetResource>::trace(visitor);
 }
 
 }  // namespace blink