Introduce base::StringSplitter

Also improve FsMount tests

Test: perfetto_unittests --getst_filter=StringSplitterTest*
Bug: 73625480
Change-Id: Ib542af6eaa8f27f0aac01c81632d6230b4d17f19
diff --git a/Android.bp b/Android.bp
index 12469e5..15f4e94 100644
--- a/Android.bp
+++ b/Android.bp
@@ -33,6 +33,7 @@
     ":perfetto_src_ipc_wire_protocol_gen",
     "src/base/file_utils.cc",
     "src/base/page_allocator.cc",
+    "src/base/string_splitter.cc",
     "src/base/thread_checker.cc",
     "src/base/unix_task_runner.cc",
     "src/base/watchdog.cc",
@@ -130,6 +131,7 @@
     "src/base/android_task_runner.cc",
     "src/base/file_utils.cc",
     "src/base/page_allocator.cc",
+    "src/base/string_splitter.cc",
     "src/base/thread_checker.cc",
     "src/base/unix_task_runner.cc",
     "src/base/watchdog.cc",
@@ -240,6 +242,7 @@
     "src/base/android_task_runner.cc",
     "src/base/file_utils.cc",
     "src/base/page_allocator.cc",
+    "src/base/string_splitter.cc",
     "src/base/test/test_task_runner.cc",
     "src/base/test/vm_test_utils.cc",
     "src/base/thread_checker.cc",
@@ -2947,6 +2950,7 @@
     ":perfetto_src_ipc_wire_protocol_gen",
     "src/base/file_utils.cc",
     "src/base/page_allocator.cc",
+    "src/base/string_splitter.cc",
     "src/base/thread_checker.cc",
     "src/base/unix_task_runner.cc",
     "src/base/watchdog.cc",
@@ -3059,6 +3063,8 @@
     "src/base/page_allocator.cc",
     "src/base/page_allocator_unittest.cc",
     "src/base/scoped_file_unittest.cc",
+    "src/base/string_splitter.cc",
+    "src/base/string_splitter_unittest.cc",
     "src/base/task_runner_unittest.cc",
     "src/base/test/test_task_runner.cc",
     "src/base/test/vm_test_utils.cc",