Adding death tests to string piece bounds checks.

These tests should ensure that bounds are being checked for string piece
functions and that these guarantees don't decay.

R=mpdenton@chromium.org
BUG=817982

Change-Id: I24f365e3b1461082fd5abc725d3f905662faeb71
Reviewed-on: https://chromium-review.googlesource.com/c/1301460
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603351}

base/strings/string_piece_unittest.cc

@@ -723,6 +723,33 @@ TEST(StringPieceTest, ConstexprCtor) {
   }
 }
 
+TEST(StringPieceTest, OutOfBoundsDeath) {
+  {
+    constexpr StringPiece piece;
+    ASSERT_DEATH_IF_SUPPORTED(piece[0], "");
+  }
+
+  {
+    constexpr StringPiece piece;
+    ASSERT_DEATH_IF_SUPPORTED(piece.front(), "");
+  }
+
+  {
+    constexpr StringPiece piece;
+    ASSERT_DEATH_IF_SUPPORTED(piece.back(), "");
+  }
+
+  {
+    StringPiece piece;
+    ASSERT_DEATH_IF_SUPPORTED(piece.remove_suffix(1), "");
+  }
+
+  {
+    StringPiece piece;
+    ASSERT_DEATH_IF_SUPPORTED(piece.remove_prefix(1), "");
+  }
+}
+
 TEST(StringPieceTest, ConstexprData) {
   {
     constexpr StringPiece piece;