Create a Lite Page bit for previews and fallback to Lo-Fi

content/public/common/previews_state.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_PUBLIC_COMMON_PREVIEWS_TYPE_H_
 #define CONTENT_PUBLIC_COMMON_PREVIEWS_TYPE_H_
 
 #include "content/common/content_export.h"
 #include "third_party/WebKit/public/platform/WebURLRequest.h"
 
 #define STATIC_ASSERT_PREVIEWS_ENUM(a, b)                   \
   static_assert(static_cast<int>(a) == static_cast<int>(b), \
                 "mismatching enums: " #a)
 
 namespace content {
 
-// The Previews state which determines whether to request a Preview version of
+// Chrome Proxy Previews header and directives.
+const char kChromeProxyContentTransformHeader[] =
+    "chrome-proxy-content-transform";
+const char kChromeProxyEmptyImageDirective[] = "empty-image";
+const char kChromeProxyLitePageDirective[] = "lite-page";
+
+typedef int PreviewsState;
+
+// The Previews types which determines whether to request a Preview version of
 // the resource. Previews are optimizations that change the format and
 // content of web pages to improve data savings and / or performance. This enum
 // determines which Previews types to request.
-enum PreviewsState {
+enum PreviewsTypes {
   PREVIEWS_UNSPECIFIED = 0,        // Let the browser process decide whether or
                                    // not to request Preview types.
   SERVER_LOFI_ON = 1 << 0,         // Request a Lo-Fi version of the resource
                                    // from the server.
   CLIENT_LOFI_ON = 1 << 1,         // Request a Lo-Fi version of the resource
                                    // from the client.
-  PREVIEWS_NO_TRANSFORM = 1 << 2,  // Explicitly forbid Previews
+  SERVER_LITE_PAGE_ON = 1 << 2,    // Request a Lite Page version of the
+                                   // resource from the server.
+  PREVIEWS_NO_TRANSFORM = 1 << 3,  // Explicitly forbid Previews
                                    // transformations.
-  PREVIEWS_OFF = 1 << 3,           // Request a normal (non-Preview) version of
+  PREVIEWS_OFF = 1 << 4,           // Request a normal (non-Preview) version of
                                    // the resource. Server transformations may
                                    // still happen if the page is heavy.
   PREVIEWS_STATE_LAST = PREVIEWS_OFF
 };
 
 // Ensure that content::PreviewsState and blink::WebURLRequest::PreviewsState
 // are kept in sync.
 STATIC_ASSERT_PREVIEWS_ENUM(PREVIEWS_UNSPECIFIED,
                             blink::WebURLRequest::PreviewsUnspecified);
 STATIC_ASSERT_PREVIEWS_ENUM(SERVER_LOFI_ON, blink::WebURLRequest::ServerLoFiOn);
 STATIC_ASSERT_PREVIEWS_ENUM(CLIENT_LOFI_ON, blink::WebURLRequest::ClientLoFiOn);
+STATIC_ASSERT_PREVIEWS_ENUM(SERVER_LITE_PAGE_ON,
+                            blink::WebURLRequest::ServerLitePageOn);
 STATIC_ASSERT_PREVIEWS_ENUM(PREVIEWS_NO_TRANSFORM,
                             blink::WebURLRequest::PreviewsNoTransform);
 STATIC_ASSERT_PREVIEWS_ENUM(PREVIEWS_OFF, blink::WebURLRequest::PreviewsOff);
 STATIC_ASSERT_PREVIEWS_ENUM(PREVIEWS_STATE_LAST,
                             blink::WebURLRequest::PreviewsStateLast);
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_COMMON_PREVIEWS_TYPE_H_