Add abilities to generate bitcode buffers from munged bitcode.

unittests/Bitcode/NaClAbbrevErrorTests.cpp

Index: unittests/Bitcode/NaClAbbrevErrorTests.cpp
diff --git a/unittests/Bitcode/NaClAbbrevErrorTests.cpp b/unittests/Bitcode/NaClAbbrevErrorTests.cpp
index 38ceb42b2e79f8737d76f117183f51434a9ddb68..a858c07f0027ee9f6453f462bcde8da0e19bf48a 100644
--- a/unittests/Bitcode/NaClAbbrevErrorTests.cpp
+++ b/unittests/Bitcode/NaClAbbrevErrorTests.cpp
@@ -75,15 +75,27 @@ TEST(MyDeathNaClAbbrevErrorTests, BadAbbreviationIndex) {
     ReplaceIndex, NaClMungedBitcode::Replace,
     4, naclbitc::TYPE_CODE_VOID, Terminator,
   };
+
+  // Show that by default, one can't write a bad abbreviation index.
   DumpMunger.setRunAsDeathTest(true);
   EXPECT_DEATH(
       DumpMunger.runTest("Bad abbreviation index 4",
                          AbbrevIndex4, array_lengthof(AbbrevIndex4)),
+      ".*Error \\(Block 17\\)\\: Uses illegal abbreviation index\\:"
+      "        4\\: \\[2\\].*");
+
+  // Show that the corresponding error is generated when reading
+  // bitcode with a bad abbreviation index.
+  DumpMunger.WriteFlags.SaveBadAbbrevIndices = true;
+  EXPECT_DEATH(
+      DumpMunger.runTest("Bad abbreviation index 4",
+                         AbbrevIndex4, array_lengthof(AbbrevIndex4)),
       ".*Fatal\\(35\\:0\\)\\: Invalid abbreviation \\# 4 defined for record.*");
 
   // Test that bitcode reader reports problem correctly.
   NaClParseBitcodeMunger Munger(BitcodeRecords,
                                 array_lengthof(BitcodeRecords), Terminator);
+  Munger.WriteFlags.SaveBadAbbrevIndices = true;

[jvoung (off chromium), 2015/05/06 22:08:09]

It looks like there you could also separately test WriteFlags.TryRecover = true
w/ SaveBadAbbrevIndices = false, based on the check

+      if (!Flags.TryToRecover && !Flags.SaveBadAbbrevIndices)
+        return false;

[Karl, 2015/05/07 20:09:18]

Added recovery cases. Also refactored the RunAsDeathTest so that it applies to
all mungers. I did this to guarantee we can see what did occurred before the
death of the test.

I also moved death tests into their own copies, so that there is no state
pollution (since the death may leave the munger in a bad state).

   EXPECT_DEATH(
       Munger.runTest("Bad abbreviation index",
                      AbbrevIndex4, array_lengthof(AbbrevIndex4), true),