[SH] Remove existing text fragment before adding new one when generating

When generating a link to text, remove existing fragments before
appending the new one(s) to the URL.

Bug: 1143676
Change-Id: Ie49818130219aa9cf1adfc06d5b919c713c58055
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2507629
Commit-Queue: sebsg <sebsg@chromium.org>
Commit-Queue: Sebastien Lalancette <seblalancette@chromium.org>
Reviewed-by: Sebastien Lalancette <seblalancette@chromium.org>
Cr-Commit-Position: refs/heads/master@{#822205}

components/shared_highlighting/core/common/text_fragments_utils.cc

@@ -83,9 +83,10 @@ GURL AppendFragmentDirectives(const GURL& base_url,
   if (new_ref.find(kFragmentsUrlDelimiter) == std::string::npos) {
     new_ref += kFragmentsUrlDelimiter;
   } else {
-    // The URL already had the :~: delimiter, so prepare appending the new
-    // fragments by appending an ampersand beforehand.
-    new_ref += "&";
+    // The URL already had the :~: delimiter, so remove what comes after before
+    // adding the new fragment(s).
+    new_ref = new_ref.substr(0, new_ref.find(kFragmentsUrlDelimiter) +
+                                    strlen(kFragmentsUrlDelimiter));
   }
 
   new_ref += fragments_string;

components/shared_highlighting/core/common/text_fragments_utils_unittest.cc

@@ -73,13 +73,25 @@ TEST(TextFragmentsUtilsTest, AppendFragmentDirectivesURLWithPoundAndValue) {
 
 TEST(TextFragmentsUtilsTest,
      AppendFragmentDirectivesURLWithPoundAndExistingFragment) {
+  GURL base_url("https://www.chromium.org/#:~:text=some%20value");
+  TextFragment test_fragment("only start");
+
+  GURL created_url = AppendFragmentDirectives(base_url, {test_fragment});
+  EXPECT_EQ(
+      "https://www.chromium.org/"
+      "#:~:text=only%20start",
+      created_url.spec());
+}
+
+TEST(TextFragmentsUtilsTest,
+     AppendFragmentDirectivesURLWithPoundAndExistingFragmentAndAnchor) {
   GURL base_url("https://www.chromium.org/#SomeAnchor:~:text=some%20value");
   TextFragment test_fragment("only start");
 
   GURL created_url = AppendFragmentDirectives(base_url, {test_fragment});
   EXPECT_EQ(
       "https://www.chromium.org/"
-      "#SomeAnchor:~:text=some%20value&text=only%20start",
+      "#SomeAnchor:~:text=only%20start",
       created_url.spec());
 }