Fixed SplitStringUsingSubstr to handle empty delimiters

Issue:
The base::SplitStringUsingSubstr does not handle the case when the
delimiter is empty. The code goes into an infinite loop in that case
as begin_index and end_index always stay 0 and we keep on adding empty
string pieces to the result. This causes a memory overflow.

Fix:
This change adds a check for the delimiter size and returns the
original input string if the size is 0.

Bug: 1062612
Change-Id: I29c184bf18df1bcc50fdb6205a7ff5fa6920148b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2108213
Commit-Queue: Siddharth Sharma <siddhash@microsoft.com>
Reviewed-by: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751476}

base/strings/string_split.cc

@@ -104,6 +104,11 @@ std::vector<OutputStringType> SplitStringUsingSubstrT(
   using size_type = typename Piece::size_type;
 
   std::vector<OutputStringType> result;
+  if (delimiter.size() == 0) {
+    result.emplace_back(input);
+    return result;
+  }
+
   for (size_type begin_index = 0, end_index = 0; end_index != Piece::npos;
        begin_index = end_index + delimiter.size()) {
     end_index = input.find(delimiter, begin_index);

base/strings/string_split_unittest.cc

@@ -218,6 +218,13 @@ TEST(SplitStringUsingSubstrTest, EmptyString) {
   EXPECT_THAT(results, ElementsAre(""));
 }
 
+TEST(SplitStringUsingSubstrTest, EmptyDelimiter) {
+  std::vector<std::string> results = SplitStringUsingSubstr(
+      "TEST", std::string(), TRIM_WHITESPACE, SPLIT_WANT_ALL);
+  ASSERT_EQ(1u, results.size());
+  EXPECT_THAT(results, ElementsAre("TEST"));
+}
+
 TEST(StringUtilTest, SplitString_Basics) {
   std::vector<std::string> r;