Fix DownloadHistoryCheck on windows continuous builder.

Currently it's flaky that a partial buffer is read through network
pipeline when the first history db record is generated.

This CL changed the observer to be able to optionally wait for a
certain number of bytes read from network IO.

Bug: 788160
Change-Id: I110653433e8c80c2dabf9f3162df99d7bb354e86
Reviewed-on: https://chromium-review.googlesource.com/790946Reviewed-by: Min Qin <qinmin@chromium.org>
Commit-Queue: Xing Liu <xingliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#519930}

chrome/browser/download/download_browsertest.cc

@@ -357,7 +357,8 @@ class HistoryObserver : public DownloadHistory::Observer {
   explicit HistoryObserver(Profile* profile)
       : profile_(profile),
         waiting_(false),
-        seen_stored_(false) {
+        seen_stored_(false),
+        minimum_received_bytes_(kNoMinimumReceivedBytes) {
     DownloadCoreServiceFactory::GetForBrowserContext(profile_)
         ->GetDownloadHistory()
         ->AddObserver(this);
@@ -370,6 +371,10 @@ class HistoryObserver : public DownloadHistory::Observer {
       service->GetDownloadHistory()->RemoveObserver(this);
   }
 
+  void set_minimum_received_bytes(int64_t minimum_received_bytes) {
+    minimum_received_bytes_ = minimum_received_bytes;
+  }
+
   void SetFilterCallback(const FilterCallback& callback) {
     callback_ = callback;
   }
@@ -379,6 +384,11 @@ class HistoryObserver : public DownloadHistory::Observer {
     if (!callback_.is_null() && (!callback_.Run(info)))
         return;
 
+    if (minimum_received_bytes_ != kNoMinimumReceivedBytes &&
+        info.received_bytes < minimum_received_bytes_) {
+      return;
+    }
+
     seen_stored_ = true;
     if (waiting_)
       base::RunLoop::QuitCurrentWhenIdleDeprecated();
@@ -399,9 +409,11 @@ class HistoryObserver : public DownloadHistory::Observer {
   }
 
  private:
+  static const int64_t kNoMinimumReceivedBytes = -1;
   Profile* profile_;
   bool waiting_;
   bool seen_stored_;
+  int64_t minimum_received_bytes_;
   FilterCallback callback_;
 
   DISALLOW_COPY_AND_ASSIGN(HistoryObserver);
@@ -1841,13 +1853,7 @@ ServerRedirectRequestHandler(const net::test_server::HttpRequest& request) {
   return std::move(response);
 }
 
-#if defined(OS_WIN)
-// https://crbug.com/788160
-#define MAYBE_DownloadHistoryCheck DISABLED_DownloadHistoryCheck
-#else
-#define MAYBE_DownloadHistoryCheck DownloadHistoryCheck
-#endif
-IN_PROC_BROWSER_TEST_F(DownloadTest, MAYBE_DownloadHistoryCheck) {
+IN_PROC_BROWSER_TEST_F(DownloadTest, DownloadHistoryCheck) {
   // Rediret to the actual download URL.
   embedded_test_server()->RegisterRequestHandler(
       base::Bind(&ServerRedirectRequestHandler));
@@ -1882,6 +1888,8 @@ IN_PROC_BROWSER_TEST_F(DownloadTest, MAYBE_DownloadHistoryCheck) {
   base::Time start(base::Time::Now());
   HistoryObserver observer(browser()->profile());
   observer.SetFilterCallback(base::Bind(&HasDataAndName));
+  observer.set_minimum_received_bytes(
+      content::SlowDownloadHttpResponse::kFirstDownloadSize);
   ui_test_utils::NavigateToURL(browser(), redirect_url);
   observer.WaitForStored();