[iOS] Crash bug fix for WebStateImpl being null during download process

This is a merge to M103. 

There's currently a bug where a user crashes during the download
process due to WebState being null. Reproducing the crash through a
unit/eg test is currently difficult since the cause of the crash seems
to be time dependent hence why there isn't a unit test accompanied with
the fix to test if it works. Existing unit tests have also been
updated to pass the tests since we can't replicate a delegate call since
the delegate is set to nil. This way, unit tests can still pass as if
the delegate existed and wasn't prematurely cancelled.

(cherry picked from commit 13df7d1)

Fixed: 1325108
Change-Id: I72a54fcddde20d95061642539c3553b0e3c219ef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3648169
Commit-Queue: Joemer Ramos <joemerramos@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1004248}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3661421
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Auto-Submit: Joemer Ramos <joemerramos@chromium.org>
Cr-Commit-Position: refs/branch-heads/5060@{#217}
Cr-Branched-From: b83393d-refs/heads/main@{#1002911}

ios/web/download/download_native_task_bridge.h

@@ -34,7 +34,7 @@ using NativeDownloadTaskCompleteCallback =
 
 // Used to set response url, content length, mimetype and http response headers
 // in CRWWkNavigationHandler so method can interact with WKWebView.
-- (void)onDownloadNativeTaskBridgeReadyForDownload:
+- (BOOL)onDownloadNativeTaskBridgeReadyForDownload:
     (DownloadNativeTaskBridge*)bridge API_AVAILABLE(ios(15));
 
 // Calls CRWWKNavigationHandlerDelegate to resume download using |webView|

ios/web/download/download_native_task_bridge.mm

@@ -153,7 +153,9 @@ - (void)download:(WKDownload*)download
     handler(_urlForDownload);
   } else {
     _startDownloadBlock = handler;
-    [_delegate onDownloadNativeTaskBridgeReadyForDownload:self];
+    if (![_delegate onDownloadNativeTaskBridgeReadyForDownload:self]) {
+      [self cancel];
+    }
   }
 }
 

ios/web/navigation/crw_wk_navigation_handler.mm

@@ -1043,8 +1043,17 @@ - (void)webView:(WKWebView*)webView
                                                           delegate:self]];
 }
 
-- (void)onDownloadNativeTaskBridgeReadyForDownload:
+// Used to set response url, content length, mimetype and http response headers
+// in CRWWkNavigationHandler so method can interact with WKWebView. Returns NO
+// if the download cannot be started.
+- (BOOL)onDownloadNativeTaskBridgeReadyForDownload:
     (DownloadNativeTaskBridge*)bridge API_AVAILABLE(ios(15)) {
+  __attribute__((objc_precise_lifetime))
+  DownloadNativeTaskBridge* nativeTaskBridge = bridge;
+  [_nativeTaskBridges removeObject:bridge];
+  if (!self.webStateImpl)
+    return NO;
+
   const GURL responseURL = net::GURLWithNSURL(bridge.response.URL);
   const int64_t contentLength = bridge.response.expectedContentLength;
   const std::string MIMEType =
@@ -1066,8 +1075,7 @@ - (void)onDownloadNativeTaskBridgeReadyForDownload:
       ->CreateNativeDownloadTask(self.webStateImpl, [NSUUID UUID].UUIDString,
                                  responseURL, HTTPMethod, contentDisposition,
                                  contentLength, MIMEType, bridge);
-
-  [_nativeTaskBridges removeObject:bridge];
+  return YES;
 }
 
 - (void)resumeDownloadNativeTask:(NSData*)data

ios/web/test/fakes/fake_native_task_bridge.mm

@@ -6,12 +6,17 @@
 
 #import "base/callback.h"
 #import "base/strings/sys_string_conversions.h"
+#import "net/base/net_errors.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
-@implementation FakeNativeTaskBridge
+@implementation FakeNativeTaskBridge {
+  void (^_startDownloadBlock)(NSURL*);
+  BOOL _observingDownloadProgress;
+  NativeDownloadTaskCompleteCallback _completeCallback;
+}
 
 @synthesize download = _download;
 @synthesize progress = _progress;
@@ -30,41 +35,81 @@ - (instancetype)initWithDownload:(WKDownload*)download
 }
 
 - (void)cancel {
-  [super cancel];
+  if (_startDownloadBlock) {
+    _startDownloadBlock(nil);
+  }
   _progress = [NSProgress progressWithTotalUnitCount:0];
 }
 
 - (void)startDownload:(const base::FilePath&)path
      progressCallback:(NativeDownloadTaskProgressCallback)progressCallback
      responseCallback:(NativeDownloadTaskResponseCallback)responseCallback
      completeCallback:(NativeDownloadTaskCompleteCallback)completeCallback {
-  [super startDownload:path
-      progressCallback:std::move(progressCallback)
-      responseCallback:std::move(responseCallback)
-      completeCallback:std::move(completeCallback)];
+  _completeCallback = std::move(completeCallback);
+  [self startObservingDownloadProgress];
+  _startDownloadBlock(self.urlForDownload);
+  _startDownloadBlock = nil;
 
   // Simulates completing a download progress
   _progress = [NSProgress progressWithTotalUnitCount:100];
 }
 
+- (void)dealloc {
+  [self stopObservingDownloadProgress];
+}
+
 #pragma mark - Private methods
 
 - (void)downloadInitialized API_AVAILABLE(ios(15)) {
   // Instantiates _startDownloadBlock, so when we call
   // startDownload:progressionHandler:completionHandler method, the block is
   // initialized.
   __weak FakeNativeTaskBridge* weakSelf = self;
-  [super download:_download
-      decideDestinationUsingResponse:_response
-                   suggestedFilename:_suggestedFilename
-                   completionHandler:^void(NSURL* url) {
-                     [weakSelf destinationDecided:url];
-                   }];
+  void (^handler)(NSURL* destination) = ^void(NSURL* url) {
+    [weakSelf destinationDecided:url];
+  };
+
+  if (self.urlForDownload) {
+    // Resuming a download.
+    [self startObservingDownloadProgress];
+    handler(self.urlForDownload);
+  } else {
+    _startDownloadBlock = handler;
+  }
 }
 
 - (void)destinationDecided:(NSURL*)url API_AVAILABLE(ios(15)) {
   _calledStartDownloadBlock = YES;
   [self downloadDidFinish:_download];
 }
 
+#pragma mark - Private methods
+
+- (void)startObservingDownloadProgress {
+  DCHECK(!_observingDownloadProgress);
+
+  _observingDownloadProgress = YES;
+  [self.progress addObserver:self
+                  forKeyPath:@"fractionCompleted"
+                     options:NSKeyValueObservingOptionNew
+                     context:nil];
+}
+
+- (void)stopObservingDownloadProgress {
+  if (_observingDownloadProgress) {
+    _observingDownloadProgress = NO;
+    [self.progress removeObserver:self
+                       forKeyPath:@"fractionCompleted"
+                          context:nil];
+  }
+}
+
+- (void)downloadDidFinish:(WKDownload*)download API_AVAILABLE(ios(15)) {
+  [self stopObservingDownloadProgress];
+  if (!_completeCallback.is_null()) {
+    web::DownloadResult download_result(net::OK);
+    std::move(_completeCallback).Run(download_result);
+  }
+}
+
 @end