Initial CL for Downloads resumption.

content/browser/loader/resource_dispatcher_host_impl.cc

Index: content/browser/loader/resource_dispatcher_host_impl.cc
diff --git a/content/browser/loader/resource_dispatcher_host_impl.cc b/content/browser/loader/resource_dispatcher_host_impl.cc
index fd945c744a5fe8c85659d748a10017c1eab5d4b0..f92401088c40aa1509a1743ad4edb50de88deec0 100644
--- a/content/browser/loader/resource_dispatcher_host_impl.cc
+++ b/content/browser/loader/resource_dispatcher_host_impl.cc
@@ -49,6 +49,7 @@
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/content_browser_client.h"
 #include "content/public/browser/download_manager.h"
+#include "content/public/browser/download_save_info.h"
 #include "content/public/browser/global_request_id.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/resource_dispatcher_host_delegate.h"
@@ -498,6 +499,9 @@ net::Error ResourceDispatcherHostImpl::BeginDownload(
     int route_id,
     bool prefer_cache,
     scoped_ptr<DownloadSaveInfo> save_info,
+    const std::string& last_modified,
+    const std::string& etag,
+    content::DownloadId download_id,
     const DownloadStartedCallback& started_callback) {
   if (is_shutdown_)
     return CallbackAndReturn(started_callback, net::ERR_INSUFFICIENT_RESOURCES);
@@ -536,6 +540,27 @@ net::Error ResourceDispatcherHostImpl::BeginDownload(
   request_id_--;
 
   const net::URLRequestContext* request_context = context->GetRequestContext();
+
+  // If we're not at the beginning of the file, retrieve only the remaining
+  // portion.
+  if (save_info->offset > 0) {
+    request->SetExtraRequestHeaderByName(
+        "Range",
+        StringPrintf("bytes=%" PRId64 "-", save_info->offset),
+        true);
+
+    // If we've asked for a range, we want to make sure that we only
+    // get that range if our current copy of the information is good.
+    if (!last_modified.empty()) {
+      request->SetExtraRequestHeaderByName("If-Unmodified-Since",
+                                           last_modified,
+                                           true);
+    }
+    if (!etag.empty()) {
+      request->SetExtraRequestHeaderByName("If-Match", etag, true);
+    }
+  }
+
   if (!request_context->job_factory()->IsHandledURL(url)) {
     VLOG(1) << "Download request for unsupported protocol: "
             << url.possibly_invalid_spec();
@@ -550,7 +575,7 @@ net::Error ResourceDispatcherHostImpl::BeginDownload(
   // |started_callback|.
   scoped_ptr<ResourceHandler> handler(
       CreateResourceHandlerForDownload(request.get(), is_content_initiated,
-                                       true, save_info.Pass(),
+                                       true, download_id, save_info.Pass(),
                                        started_callback));
 
   BeginRequestInternal(request.Pass(), handler.Pass());
@@ -581,10 +606,11 @@ ResourceDispatcherHostImpl::CreateResourceHandlerForDownload(
     net::URLRequest* request,
     bool is_content_initiated,
     bool must_download,
+    DownloadId id,
     scoped_ptr<DownloadSaveInfo> save_info,
     const DownloadResourceHandler::OnStartedCallback& started_cb) {
   scoped_ptr<ResourceHandler> handler(
-      new DownloadResourceHandler(request, started_cb, save_info.Pass()));
+      new DownloadResourceHandler(id, request, started_cb, save_info.Pass()));
   if (delegate_) {
     const ResourceRequestInfo* request_info(
         ResourceRequestInfo::ForRequest(request));