[SH iOS] Adding Scroll to Text feature

This feature splits the scroll to text functionality off of the Shared
Highlighting flag. This is needed because:

* The Scroll-to-text portion will be launching first
* The Scroll-to-text portion is being built in //ios/web to enable
  external usage.

Bug: 1099268
Change-Id: I60cbe5d20907d4889aa46a051ec335dfe55b59b4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2329947Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Tommy Martino <tmartino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#793675}

chrome/browser/flag-metadata.json

@@ -3833,6 +3833,11 @@
     "owners": [ "bingler", "chlily" ],
     "expiry_milestone": 90
   },
+  {
+    "name": "scroll-to-text-ios",
+    "owners": [ "tmartino" ],
+    "expiry_milestone": 90
+  },
   {
     "name": "scroll-unification",
     "owners": [ "bokan@chromium.org", "input-dev@chromium.org" ],

ios/chrome/browser/flags/about_flags.mm

@@ -680,6 +680,9 @@ const flags_ui::FeatureEntry kFeatureEntries[] = {
      flag_descriptions::kEnableFullPageScreenshotName,
      flag_descriptions::kEnableFullPageScreenshotDescription, flags_ui::kOsIos,
      FEATURE_VALUE_TYPE(kEnableFullPageScreenshot)},
+    {"scroll-to-text-ios", flag_descriptions::kScrollToTextIOSName,
+     flag_descriptions::kScrollToTextIOSDescription, flags_ui::kOsIos,
+     FEATURE_VALUE_TYPE(web::features::kScrollToTextIOS)},
 };
 
 bool SkipConditionalFeatureEntry(const flags_ui::FeatureEntry& entry) {

ios/chrome/browser/flags/ios_chrome_flag_descriptions.cc

@@ -421,6 +421,12 @@ const char kSaveCardInfobarMessagesUIName[] = "Save Card Infobar Messages UI";
 const char kSaveCardInfobarMessagesUIDescription[] =
     "When enabled, Save Card Infobar uses the new Messages UI.";
 
+const char kScrollToTextIOSName[] = "Enable Scroll to Text";
+const char kScrollToTextIOSDescription[] =
+    "When enabled, opening a URL with a text fragment (e.g., "
+    "example.com/#:~:text=examples) will cause matching text in the page to be "
+    "highlighted and scrolled into view.";
+
 const char kSendTabToSelfName[] = "Send tab to self";
 const char kSendTabToSelfDescription[] =
     "Allows users to receive tabs that were pushed from another of their "
@@ -438,9 +444,8 @@ const char kSettingsRefreshDescription[] =
 
 const char kSharedHighlightingIOSName[] = "Enable Shared Highlighting features";
 const char kSharedHighlightingIOSDescription[] =
-    "Enables support for Text Fragments (scroll-to-text based on URL "
-    "directive) and a Link to Text option in the Edit Menu which generates "
-    "these URLs.";
+    "Adds a Link to Text option in the Edit Menu which generates URLs with a "
+    "text fragment. Works best with the #scroll-to-text-ios flag.";
 
 const char kShowAutofillTypePredictionsName[] = "Show Autofill predictions";
 const char kShowAutofillTypePredictionsDescription[] =

ios/chrome/browser/flags/ios_chrome_flag_descriptions.h

@@ -366,6 +366,10 @@ extern const char kSafetyCheckIOSDescription[];
 extern const char kSaveCardInfobarMessagesUIName[];
 extern const char kSaveCardInfobarMessagesUIDescription[];
 
+// Title and description for the flag to enable the Scroll to Text feature.
+extern const char kScrollToTextIOSName[];
+extern const char kScrollToTextIOSDescription[];
+
 // Title and description for the flag to enable the send tab to self receiving
 // feature.
 extern const char kSendTabToSelfName[];
@@ -381,7 +385,7 @@ extern const char kSettingsRefreshName[];
 extern const char kSettingsRefreshDescription[];
 
 // Title and description for the flag to enable Shared Highlighting (Link to
-// Text Edit Menu option and Text Fragments web behavior).
+// Text Edit Menu option).
 extern const char kSharedHighlightingIOSName[];
 extern const char kSharedHighlightingIOSDescription[];
 

ios/chrome/browser/ui/ui_feature_flags.h

@@ -65,8 +65,8 @@ extern const base::Feature kSafetyCheckIOS;
 // Feature flag to enable new illustrations and UI on empty states.
 extern const base::Feature kIllustratedEmptyStates;
 
-// Feature flag to enable Shared Highlighting (Text Fragments/scroll-to-text
-// and Link to Text features).
+// Feature flag to enable Shared Highlighting (Link to Text). Also enable
+// kScrollToTextIOS to successfully open these links.
 extern const base::Feature kSharedHighlightingIOS;
 
 // Feature flag that enables taking fullpage screenshots of a webpage.

ios/web/common/features.h

@@ -57,6 +57,12 @@ extern const base::Feature kIOSLookalikeUrlNavigationSuggestionsUI;
 // the URL.
 extern const base::Feature kAddWebContentDropInteraction;
 
+// When enabled, opening a URL with a text fragment (e.g.,
+// example.com/#:~:text=examples) will cause matching text in the page to be
+// highlighted and scrolled into view.
+// See also: https://wicg.github.io/scroll-to-text-fragment/
+extern const base::Feature kScrollToTextIOS;
+
 // When true, for each navigation, the default user agent is chosen by the
 // WebClient GetDefaultUserAgent() method. If it is false, the mobile version
 // is requested by default.

ios/web/common/features.mm

@@ -48,6 +48,9 @@ const base::Feature kIOSLookalikeUrlNavigationSuggestionsUI{
 const base::Feature kAddWebContentDropInteraction{
     "AddWebContentDropInteraction", base::FEATURE_DISABLED_BY_DEFAULT};
 
+const base::Feature kScrollToTextIOS{"ScrollToTextIOS",
+                                     base::FEATURE_DISABLED_BY_DEFAULT};
+
 bool UseWebClientDefaultUserAgent() {
   if (@available(iOS 13, *)) {
     return base::FeatureList::IsEnabled(kUseDefaultUserAgentInWebClient);