Document some dex2oat command line options.

Also process option `--dump-cfg-append` correctly.

Test: m build-art-host
Change-Id: I062154c267c1a6eec22af42d985f19a555bdf4ca
diff --git a/dex2oat/dex2oat.cc b/dex2oat/dex2oat.cc
index ea82133..9fd42d2 100644
--- a/dex2oat/dex2oat.cc
+++ b/dex2oat/dex2oat.cc
@@ -349,23 +349,23 @@
   UsageError("  --profile-file-fd=<number>: same as --profile-file but accepts a file descriptor.");
   UsageError("      Cannot be used together with --profile-file.");
   UsageError("");
-  UsageError("  --swap-file=<file-name>:  specifies a file to use for swap.");
+  UsageError("  --swap-file=<file-name>: specifies a file to use for swap.");
   UsageError("      Example: --swap-file=/data/tmp/swap.001");
   UsageError("");
-  UsageError("  --swap-fd=<file-descriptor>:  specifies a file to use for swap (by descriptor).");
+  UsageError("  --swap-fd=<file-descriptor>: specifies a file to use for swap (by descriptor).");
   UsageError("      Example: --swap-fd=10");
   UsageError("");
-  UsageError("  --swap-dex-size-threshold=<size>:  specifies the minimum total dex file size in");
+  UsageError("  --swap-dex-size-threshold=<size>: specifies the minimum total dex file size in");
   UsageError("      bytes to allow the use of swap.");
   UsageError("      Example: --swap-dex-size-threshold=1000000");
   UsageError("      Default: %zu", kDefaultMinDexFileCumulativeSizeForSwap);
   UsageError("");
-  UsageError("  --swap-dex-count-threshold=<count>:  specifies the minimum number of dex files to");
+  UsageError("  --swap-dex-count-threshold=<count>: specifies the minimum number of dex files to");
   UsageError("      allow the use of swap.");
   UsageError("      Example: --swap-dex-count-threshold=10");
   UsageError("      Default: %zu", kDefaultMinDexFilesForSwap);
   UsageError("");
-  UsageError("  --very-large-app-threshold=<size>:  specifies the minimum total dex file size in");
+  UsageError("  --very-large-app-threshold=<size>: specifies the minimum total dex file size in");
   UsageError("      bytes to consider the input \"very large\" and punt on the compilation.");
   UsageError("      Example: --very-large-app-threshold=100000000");
   UsageError("");
@@ -380,6 +380,14 @@
   UsageError("");
   UsageError("  --force-determinism: force the compiler to emit a deterministic output.");
   UsageError("");
+  UsageError("  --dump-cfg=<cfg-file>: dump control-flow graphs (CFGs) to specified file.");
+  UsageError("      Example: --dump-cfg=output.cfg");
+  UsageError("");
+  UsageError("  --dump-cfg-append: when dumping CFGs to an existing file, append new CFG data to");
+  UsageError("      existing data (instead of overwriting existing data with new data, which is");
+  UsageError("      the default behavior). This option is only meaningful when used with");
+  UsageError("      --dump-cfg.");
+  UsageError("");
   UsageError("  --classpath-dir=<directory-path>: directory used to resolve relative class paths.");
   UsageError("");
   std::cerr << "See log for usage error information\n";