[base] Remove base::StringPiece::as_string() usages.

This API is not compliant with absl::/std::string_view.

Bug: 1049498
Change-Id: If0c9b53c8dca314a6c66d82390734352f9f965de
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2855291
Commit-Queue: Peter Kasting <[email protected]>
Commit-Queue: Dmitry Gozman <[email protected]>
Auto-Submit: Peter Kasting <[email protected]>
Reviewed-by: Dmitry Gozman <[email protected]>
Cr-Commit-Position: refs/heads/master@{#877178}
diff --git a/content/common/set_process_title_linux_unittest.cc b/content/common/set_process_title_linux_unittest.cc
index 5c47e2aa..6e5a26c1e 100644
--- a/content/common/set_process_title_linux_unittest.cc
+++ b/content/common/set_process_title_linux_unittest.cc
@@ -7,6 +7,7 @@
 
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
+#include "base/strings/string_piece.h"
 #include "base/strings/string_util.h"
 #include "content/common/set_process_title_linux.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -25,7 +26,7 @@
   // "title\0"          (on Linux 5.3--)
   //
   // For unit tests, just trim trailing null characters to support all cases.
-  return base::TrimString(cmdline, kNullChr, base::TRIM_TRAILING).as_string();
+  return std::string(base::TrimString(cmdline, kNullChr, base::TRIM_TRAILING));
 }
 
 TEST(SetProcTitleLinuxTest, Simple) {