Revert "Fix DownloadManagerTestCase flakiness."

This reverts commit eabc228b.

Reason for revert: May have caused a compile error that closed the tree: https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/ios-webview/2197

Original change's description:
> Fix DownloadManagerTestCase flakiness.
> 
> On iOS 12 URLSession:dataTask:didReceiveData: delegate method can be
> called when task is in NSURLSessionTaskStateCompleted state. This
> resulted in extra URLFetcherResponseWriter::Finish call (one from
> didReceiveData: and one from didCompleteWithError:).
> URLFetcherResponseWriter::Finish DCHECKs if Finish is called twice, so
> the test was flaky.
> 
> This CL changes DownloadTaskImpl to only call
> URLFetcherResponseWriter::Finish from didCompleteWithError:.
> 
> Bug: 873204
> Change-Id: Ie6b8757e2c5c5d35da088fd108d92ee3ed13244d
> Reviewed-on: https://chromium-review.googlesource.com/c/1354233
> Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
> Commit-Queue: Eugene But <eugenebut@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#612249}

TBR=sdefresne@chromium.org,eugenebut@chromium.org

Change-Id: I1f7e7620911c73ce1f497fb6ae7b09ed16a2547f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 873204
Reviewed-on: https://chromium-review.googlesource.com/c/1355600Reviewed-by: Sebastien Seguin-Gagnon <sebsg@chromium.org>
Commit-Queue: Sebastien Seguin-Gagnon <sebsg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612251}

ios/web/download/download_task_impl.mm

@@ -33,11 +33,8 @@ using web::WebThread;
 
 namespace {
 
-// Updates DownloadTaskImpl properties. |terminal_callback| is true if this is
-// the last update for this DownloadTaskImpl.
-using PropertiesBlock = void (^)(NSURLSessionTask*,
-                                 NSError*,
-                                 bool terminal_callback);
+// Updates DownloadTaskImpl properties.
+using PropertiesBlock = void (^)(NSURLSessionTask*, NSError*);
 // Writes buffer and calls |completionHandler| when done.
 using DataBlock = void (^)(scoped_refptr<net::IOBufferWithSize> buffer,
                            void (^completionHandler)());
@@ -117,8 +114,7 @@ int GetTaskPercentComplete(NSURLSessionTask* task) {
   base::PostTaskWithTraits(FROM_HERE, {WebThread::UI}, base::BindOnce(^{
                              CRWURLSessionDelegate* strongSelf = weakSelf;
                              if (strongSelf.propertiesBlock)
-                               strongSelf.propertiesBlock(
-                                   task, error, /*terminal_callback=*/true);
+                               strongSelf.propertiesBlock(task, error);
                            }));
 }
 
@@ -148,8 +144,7 @@ int GetTaskPercentComplete(NSURLSessionTask* task) {
   base::PostTaskWithTraits(FROM_HERE, {WebThread::UI}, base::BindOnce(^{
                              CRWURLSessionDelegate* strongSelf = weakSelf;
                              if (strongSelf.propertiesBlock)
-                               weakSelf.propertiesBlock(
-                                   task, nil, /*terminal_callback=*/false);
+                               weakSelf.propertiesBlock(task, nil);
                            }));
 }
 
@@ -343,8 +338,7 @@ NSURLSession* DownloadTaskImpl::CreateSession(NSString* identifier) {
   DCHECK(identifier.length);
   base::WeakPtr<DownloadTaskImpl> weak_this = weak_factory_.GetWeakPtr();
   id<NSURLSessionDataDelegate> session_delegate = [[CRWURLSessionDelegate alloc]
-      initWithPropertiesBlock:^(NSURLSessionTask* task, NSError* error,
-                                BOOL terminal_callback) {
+      initWithPropertiesBlock:^(NSURLSessionTask* task, NSError* error) {
         if (!weak_this.get()) {
           return;
         }
@@ -367,7 +361,7 @@ NSURLSession* DownloadTaskImpl::CreateSession(NSString* identifier) {
               static_cast<NSHTTPURLResponse*>(task.response).statusCode;
         }
 
-        if (!terminal_callback) {
+        if (task.state != NSURLSessionTaskStateCompleted) {
           OnDownloadUpdated();
           // Download is still in progress, nothing to do here.
           return;