Autoscroll new background tabs on iPad

On iPads, when many tabs are open, additional tabs opened in the background
(through the context menu) will collapse together and remain hidden. Users will
have to manually scroll through to see newly opened ones.

This CL fixes the issue by enabling the scenario that every time a new tab is
inserted, we auto scroll the tab strip view to make it immediately visible.

BUG=228419

Review-Url: https://codereview.chromium.org/2611003002
Cr-Commit-Position: refs/heads/master@{#442106}

ios/chrome/browser/about_flags.mm

@@ -98,6 +98,11 @@ void AppendSwitchesFromExperimentalSettings(base::CommandLine* command_line) {
                                     BUILDFLAG(GOOGLE_TEST_OAUTH_CLIENT_SECRET));
   }
 
+  // Populate command line flag for the tab strip auto scroll new tabs
+  // experiment from the configuration plist.
+  if ([defaults boolForKey:@"TabStripAutoScrollNewTabsDisabled"])
+    command_line->AppendSwitch(switches::kDisableTabStripAutoScrollNewTabs);
+
   // Populate command line flag for the Tab Switcher experiment from the
   // configuration plist.
   NSString* enableTabSwitcher = [defaults stringForKey:@"EnableTabSwitcher"];

ios/chrome/browser/chrome_switches.cc

@@ -49,6 +49,10 @@ const char kDisableQRScanner[] = "disable-qr-scanner";
 // Disables the Spotlight actions.
 const char kDisableSpotlightActions[] = "disable-spotlight-actions";
 
+// Disables the tab strip auto scroll new tabs.
+const char kDisableTabStripAutoScrollNewTabs[] =
+    "disable-tab-strip-autoscroll-new-tabs";
+
 // Disables the tab switcher.
 const char kDisableTabSwitcher[] = "disable-tab-switcher";
 

ios/chrome/browser/chrome_switches.h

@@ -21,6 +21,7 @@ extern const char kDisableOfflineAutoReload[];
 extern const char kDisablePaymentRequest[];
 extern const char kDisableQRScanner[];
 extern const char kDisableSpotlightActions[];
+extern const char kDisableTabStripAutoScrollNewTabs[];
 extern const char kDisableTabSwitcher[];
 extern const char kDisableIOSPhysicalWeb[];
 extern const char kDisableDownloadImageRenaming[];

ios/chrome/browser/experimental_flags.h

@@ -106,6 +106,9 @@ bool IsSpotlightActionsEnabled();
 // Whether startup crash is enabled.
 bool IsStartupCrashEnabled();
 
+// Whether or not the tab strip scrolls new tabs to be visible.
+bool IsTabStripAutoScrollNewTabsEnabled();
+
 // Whether the Tab Switcher is enabled for iPad or not.
 bool IsTabSwitcherEnabled();
 

ios/chrome/browser/experimental_flags.mm

@@ -273,6 +273,11 @@ bool IsStartupCrashEnabled() {
   return [[NSUserDefaults standardUserDefaults] boolForKey:kEnableStartupCrash];
 }
 
+bool IsTabStripAutoScrollNewTabsEnabled() {
+  base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
+  return !command_line->HasSwitch(switches::kDisableTabStripAutoScrollNewTabs);
+}
+
 bool IsTabSwitcherEnabled() {
   // Check if the experimental flag is forced off.
   base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();

ios/chrome/browser/resources/Settings.bundle/Experimental.plist

@@ -36,6 +36,22 @@
 				<string>Disabled</string>
 			</array>
 		</dict>
+		<dict>
+			<key>Type</key>
+			<string>PSGroupSpecifier</string>
+			<key>Title</key>
+			<string>iPad Tab Strip</string>
+		</dict>
+		<dict>
+			<key>Type</key>
+			<string>PSToggleSwitchSpecifier</string>
+			<key>Title</key>
+			<string>Disable Tab Strip Auto Scroll New Tabs</string>
+			<key>Key</key>
+			<string>TabStripAutoScrollNewTabsDisabled</string>
+			<key>DefaultValue</key>
+			<false/>
+		</dict>
 		<dict>
 			<key>Type</key>
 			<string>PSGroupSpecifier</string>

ios/chrome/browser/ui/tabs/tab_strip_controller.mm

@@ -315,9 +315,11 @@ const CGFloat kNewTabButtonBottomOffsetHighRes = 2.0;
 
 // Updates the content offset of the tab strip view in order to keep the
 // selected tab view visible.
-// Content offset adjustement is only needed/performed in compact mode.
+// Content offset adjustement is only needed/performed in compact mode or
+// regular mode for newly opened tabs.
 // This method must be called with a valid |tabIndex|.
-- (void)updateContentOffsetForTabIndex:(NSUInteger)tabIndex;
+- (void)updateContentOffsetForTabIndex:(NSUInteger)tabIndex
+                              isNewTab:(BOOL)isNewTab;
 
 // Update the frame of the tab strip view (scrollview) frame, content inset and
 // toggle buttons states depending on the current layout mode.
@@ -639,7 +641,7 @@ const CGFloat kNewTabButtonBottomOffsetHighRes = 2.0;
     [currentTab updateSnapshotWithOverlay:YES visibleFrameOnly:YES];
   }
   [_tabModel setCurrentTab:tappedTab];
-  [self updateContentOffsetForTabIndex:index];
+  [self updateContentOffsetForTabIndex:index isNewTab:NO];
 }
 
 - (void)closeTab:(id)sender {
@@ -943,7 +945,7 @@ const CGFloat kNewTabButtonBottomOffsetHighRes = 2.0;
 
   [self updateContentSizeAndRepositionViews];
   [self setNeedsLayoutWithAnimation];
-  [self updateContentOffsetForTabIndex:modelIndex];
+  [self updateContentOffsetForTabIndex:modelIndex isNewTab:YES];
 }
 
 // Observer method.
@@ -1250,9 +1252,39 @@ const CGFloat kNewTabButtonBottomOffsetHighRes = 2.0;
   return IsCompactTablet() ? kMinTabWidthForCompactLayout : kMinTabWidth;
 }
 
-- (void)updateContentOffsetForTabIndex:(NSUInteger)tabIndex {
+- (void)updateContentOffsetForTabIndex:(NSUInteger)tabIndex
+                              isNewTab:(BOOL)isNewTab {
   DCHECK_NE(NSNotFound, static_cast<NSInteger>(tabIndex));
 
+  if (experimental_flags::IsTabStripAutoScrollNewTabsEnabled() && isNewTab) {
+    // The following code calculates the amount of scroll needed to make
+    // |tabIndex| visible in the "virtual" coordinate system, where root is x=0
+    // and it contains all the tabs laid out as if the tabstrip was infinitely
+    // long. The amount of scroll is calculated as a desired length that it is
+    // just large enough to contain all the tabs to the left of |tabIndex|, with
+    // the standard overlap.
+    NSUInteger numNonClosingTabsToLeft = 0;
+    NSUInteger i = 0;
+    for (TabView* tab in _tabArray.get()) {
+      if ([_closingTabs containsObject:tab])
+        ++i;
+
+      if (i == tabIndex)
+        break;
+
+      ++numNonClosingTabsToLeft;
+      ++i;
+    }
+
+    const CGFloat tabHeight = CGRectGetHeight([_tabStripView bounds]);
+    CGRect scrollRect =
+        CGRectMake(_currentTabWidth * numNonClosingTabsToLeft -
+                       ([self tabOverlap] * (numNonClosingTabsToLeft - 1)),
+                   0, _currentTabWidth, tabHeight);
+    [_tabStripView scrollRectToVisible:scrollRect animated:YES];
+    return;
+  }
+
   if (IsCompactTablet()) {
     if (tabIndex == [_tabArray count] - 1) {
       const CGFloat tabStripAvailableSpace =
@@ -1603,7 +1635,7 @@ const CGFloat kNewTabButtonBottomOffsetHighRes = 2.0;
   [self updateContentSizeAndRepositionViews];
   NSUInteger selectedModelIndex = [_tabModel indexOfTab:[_tabModel currentTab]];
   if (selectedModelIndex != NSNotFound) {
-    [self updateContentOffsetForTabIndex:selectedModelIndex];
+    [self updateContentOffsetForTabIndex:selectedModelIndex isNewTab:NO];
   }
 }