DevTools: Show error message when invalid pattern is entered in Framework...

DevTools: Show error message when invalid pattern is entered in Framework Blackbox in settings pane.

This change adds error messages in pattern validator. Below are the list of error messages:
- Pattern cannot be empty
- Pattern already exists
- Pattern must be a valid regular expression

Gif showing error messages https://imgur.com/wyIv4VR

Bug: 963183
Change-Id: I2c814ea576f7aa6f2093d78ae60428e9f6c12acf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1695982Reviewed-by: Joel Einbinder <einbinder@chromium.org>
Commit-Queue: Chandani Shrestha <chshrest@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#681939}

third_party/blink/renderer/devtools/front_end/settings/FrameworkBlackboxSettingsTab.js

@@ -158,9 +158,13 @@ Settings.FrameworkBlackboxSettingsTab = class extends UI.VBox {
     function patternValidator(item, index, input) {
       const pattern = input.value.trim();
       const patterns = this._setting.getAsArray();
+
+      if (!pattern.length)
+        return {valid: false, errorMessage: ls`Pattern cannot be empty`};
+
       for (let i = 0; i < patterns.length; ++i) {
         if (i !== index && patterns[i].pattern === pattern)
-          return {valid: false};
+          return {valid: false, errorMessage: ls`Pattern already exists`};
       }
 
       let regex;
@@ -168,7 +172,10 @@ Settings.FrameworkBlackboxSettingsTab = class extends UI.VBox {
         regex = new RegExp(pattern);
       } catch (e) {
       }
-      return {valid: !!(pattern && regex)};
+      if (!regex)
+        return {valid: false, errorMessage: ls`Pattern must be a valid regular expression`};
+      else
+        return {valid: true};
     }
 
     /**

third_party/blink/renderer/devtools/front_end/settings/settings_strings.grdp

@@ -12,6 +12,9 @@
   <message name="IDS_DEVTOOLS_331f303e56b067dd84abf94c3bd349c4" desc="Header text content in Framework Blackbox Settings Tab of the Settings">
     Framework Blackboxing
   </message>
+  <message name="IDS_DEVTOOLS_34fbf59db640eda5a3c07d59333f1d18" desc="Error message in Framework Blackbox settings pane that declares pattern must not be empty">
+    Pattern cannot be empty
+  </message>
   <message name="IDS_DEVTOOLS_4829262cecb9828817b33e0f9c907f91" desc="Text in Settings Screen of the Settings">
     Experiments
   </message>
@@ -21,6 +24,9 @@
   <message name="IDS_DEVTOOLS_57391192dfa1f247ad015a0fe2eca48e" desc="Aria accessible name in Framework Blackbox Settings Tab of the Settings">
     Pattern
   </message>
+  <message name="IDS_DEVTOOLS_87ae3156c118350d6b13cdebc37485e9" desc="Error message in Framework Blackbox settings pane that declares pattern must be a valid regular expression">
+    Pattern must be a valid regular expression
+  </message>
   <message name="IDS_DEVTOOLS_89bacc9715d030658f2602ce65426a7f" desc="Warning text content in Settings Screen of the Settings">
     WARNING:
   </message>
@@ -45,6 +51,9 @@
   <message name="IDS_DEVTOOLS_d2ef7dcdede23820e315ca1c3425ba4f" desc="Text in Framework Blackbox Settings Tab of the Settings">
     Debugger will skip through the scripts and will not stop on exceptions thrown by them.
   </message>
+  <message name="IDS_DEVTOOLS_dd08f9d5ae3e9ba421754fd31db1a44a" desc="Error message in Framework Blackbox settings pane that declares pattern already exits">
+    Pattern already exists
+  </message>
   <message name="IDS_DEVTOOLS_e3b2f7d0af9c89f5ea504968ffcd2ef0" desc="Message text content in Settings Screen of the Settings">
     These experiments could be dangerous and may require restart.
   </message>