Add Blink support for showing image placeholders using range requests.

third_party/WebKit/Source/core/fetch/FetchRequest.h

 /*
  * Copyright (C) 2012 Google, Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 31 matching lines @@
 class CORE_EXPORT FetchRequest {
   STACK_ALLOCATED();
 
  public:
   enum DeferOption { NoDefer, LazyLoad, IdleLoad };
   enum OriginRestriction {
     UseDefaultOriginRestrictionForType,
     RestrictToSameOrigin,
     NoOriginRestriction
   };
+  enum PlaceholderImageRequestType {
+    DisallowPlaceholder = 0,  // The requested image must not be a placeholder.
+    AllowPlaceholder,         // The image is allowed to be a placeholder.
+  };
 
   struct ResourceWidth {
     DISALLOW_NEW();
     float width;
     bool isSet;
 
     ResourceWidth() : width(0), isSet(false) {}
   };
 
   FetchRequest(const ResourceRequest&,
@@ skipping 54 matching lines @@
   void setContentSecurityPolicyNonce(const String& nonce) {
     m_options.contentSecurityPolicyNonce = nonce;
   }
 
   void setParserDisposition(ParserDisposition parserDisposition) {
     m_options.parserDisposition = parserDisposition;
   }
 
   void makeSynchronous();
 
+  PlaceholderImageRequestType placeholderImageRequestType() const {
+    return m_placeholderImageRequestType;
+  }
+
+  // Configures the request to load an image placeholder if the request is
+  // eligible (e.g. the url's protocol is HTTP, etc.). If this request is
+  // non-eligible, this method doesn't modify the ResourceRequest. Calling this
+  // method sets m_placeholderImageRequestType to the appropriate value.
+  void setAllowImagePlaceholder();
+
  private:
   ResourceRequest m_resourceRequest;
   String m_charset;
   ResourceLoaderOptions m_options;
   bool m_forPreload;
   bool m_linkPreload;
   double m_preloadDiscoveryTime;
   DeferOption m_defer;
   OriginRestriction m_originRestriction;
   ResourceWidth m_resourceWidth;
   ClientHintsPreferences m_clientHintPreferences;
+  PlaceholderImageRequestType m_placeholderImageRequestType;
 };
 
 }  // namespace blink
 
 #endif