[iOS] Maintain User's Scroll Position in Full Page Screenshots

Only doable on iOS 14+ since on iOS 13 we're using a different "page
size", resulting in a page with different width (and height).

Bug: 1131558
Change-Id: Idf3f10d77787f2513ed37b258a69901e6891cb30
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2426963
Commit-Queue: Sebastien Lalancette <seblalancette@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810596}

ios/chrome/browser/screenshot/screenshot_delegate.mm

@@ -7,6 +7,8 @@
 #import "ios/chrome/browser/main/browser.h"
 #import "ios/chrome/browser/ui/main/browser_interface_provider.h"
 #import "ios/chrome/browser/web_state_list/web_state_list.h"
+#import "ios/web/public/ui/crw_web_view_proxy.h"
+#import "ios/web/public/ui/crw_web_view_scroll_view_proxy.h"
 #import "ios/web/public/web_state.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
@@ -52,9 +54,23 @@
     return;
   }
 
+  CGRect webViewFrame = CGRectZero;
+  if (@available(iOS 14, *)) {
+    // We can determine the viewed frame for PDFs generated on iOS 14+. Use it
+    // to maintain scroll position in the screenshot editing tool.
+    id<CRWWebViewProxy> webProxy = webState->GetWebViewProxy();
+    CRWWebViewScrollViewProxy* scrollProxy = webProxy.scrollViewProxy;
+    CGPoint contentOffset = scrollProxy.contentOffset;
+    CGSize contentSize = scrollProxy.contentSize;
+    webViewFrame = scrollProxy.frame;
+    webViewFrame.origin.x = contentOffset.x;
+    webViewFrame.origin.y =
+        contentSize.height - webViewFrame.size.height - contentOffset.y;
+  }
+
   base::OnceCallback<void(NSData*)> callback =
       base::BindOnce(^(NSData* pdfDoumentData) {
-        completionHandler(pdfDoumentData, 0, CGRectZero);
+        completionHandler(pdfDoumentData, 0, webViewFrame);
       });
 
   webState->CreateFullPagePdf(std::move(callback));

ios/chrome/browser/screenshot/screenshot_delegate_unittest.mm

@@ -12,6 +12,8 @@
 #import "ios/chrome/browser/web_state_list/web_state_opener.h"
 #import "ios/web/public/test/fakes/test_web_state.h"
 #import "ios/web/public/test/web_task_environment.h"
+#import "ios/web/public/ui/crw_web_view_proxy.h"
+#import "ios/web/public/ui/crw_web_view_scroll_view_proxy.h"
 #import "testing/platform_test.h"
 #import "third_party/ocmock/OCMock/OCMock.h"
 
@@ -51,6 +53,31 @@ TEST_F(ScreenshotDelegateTest, ScreenshotService) {
     auto web_state = std::make_unique<web::TestWebState>();
     TestBrowser browser;
 
+    CRWWebViewScrollViewProxy* scroll_view_proxy =
+        [[CRWWebViewScrollViewProxy alloc] init];
+    UIScrollView* scroll_view = [[UIScrollView alloc] init];
+    [scroll_view_proxy setScrollView:scroll_view];
+    id web_view_proxy_mock = OCMProtocolMock(@protocol(CRWWebViewProxy));
+    [[[web_view_proxy_mock stub] andReturn:scroll_view_proxy] scrollViewProxy];
+    web_state->SetWebViewProxy(web_view_proxy_mock);
+
+    // Fake scroll_view contentOffset, contentSize and frame.
+    CGPoint content_offset = CGPointMake(10.0, 15.0);
+    CGSize content_size = CGSizeMake(425, 4000);
+    CGRect frame = CGRectMake(0, 0, 375, 812);
+    scroll_view.contentOffset = content_offset;
+    scroll_view.contentSize = content_size;
+    scroll_view.frame = frame;
+
+    CGRect expected_rect_in_page = CGRectZero;
+
+    if (@available(iOS 14, *)) {
+      expected_rect_in_page =
+          CGRectMake(content_offset.x,
+                     content_size.height - frame.size.height - content_offset.y,
+                     frame.size.width, frame.size.height);
+    }
+
     // Insert the web_state into the Browser.
     int insertion_index = browser.GetWebStateList()->InsertWebState(
         WebStateList::kInvalidIndex, std::move(web_state),
@@ -65,16 +92,18 @@ TEST_F(ScreenshotDelegateTest, ScreenshotService) {
 
     createScreenshotDelegate();
 
-    __block bool callback_ran = false;
+    __block int nbCalls = 0;
     [screenshotDelegate_ screenshotService:screenshot_service_
         generatePDFRepresentationWithCompletion:^(NSData* PDFData,
                                                   NSInteger indexOfCurrentPage,
                                                   CGRect rectInCurrentPage) {
           EXPECT_TRUE(PDFData);
-          callback_ran = true;
+          EXPECT_TRUE(
+              CGRectEqualToRect(expected_rect_in_page, rectInCurrentPage));
+          ++nbCalls;
         }];
 
-    EXPECT_TRUE(callback_ran);
+    EXPECT_EQ(1, nbCalls);
   }
 }