[iOS] Adding an Unknown LinkGenerationError Value

This value will be mainly used when facing parsing failures when
converting responses from the text-fragments-polyfill JavaScript
library used on iOS.

Bug: 1136043
Change-Id: I2af25b336944a5ac4f7258de75aeec8f73b46ef4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2499084Reviewed-by: sebsg <sebsg@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Commit-Queue: Sebastien Lalancette <seblalancette@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820907}

components/shared_highlighting/core/common/shared_highlighting_metrics.h

@@ -21,11 +21,14 @@ enum class LinkGenerationError {
   kEmptySelection = 5,
 
   // Android specific.
-  kTabHidden = 5,
-  kOmniboxNavigation = 6,
-  kTabCrash = 7,
+  kTabHidden = 6,
+  kOmniboxNavigation = 7,
+  kTabCrash = 8,
 
-  kMaxValue = kTabCrash
+  // Catch-all bucket.
+  kUnknown = 9,
+
+  kMaxValue = kUnknown
 };
 
 // These values are persisted to logs. Entries should not be renumbered and

third_party/blink/renderer/core/page/scrolling/text_fragment_selector_generator.h

@@ -46,7 +46,9 @@ class CORE_EXPORT TextFragmentSelectorGenerator final
     kOmniboxNavigation,
     kTabCrash,
 
-    kMaxValue = kTabCrash
+    kUnknown,
+
+    kMaxValue = kUnknown
   };
   explicit TextFragmentSelectorGenerator() = default;
 

tools/metrics/histograms/enums.xml

@@ -40843,6 +40843,7 @@ Called by update_gpu_driver_bug_workaround_entries.py.-->
   <int value="6" label="Tab hidden"/>
   <int value="7" label="Omnibox navigation"/>
   <int value="8" label="Tab crash"/>
+  <int value="9" label="Unknown"/>
 </enum>
 
 <enum name="LinkMonitorFailureType">