Add unittests for different transport security state generator components.

net/tools/transport_security_state_generator/BUILD.gn

Index: net/tools/transport_security_state_generator/BUILD.gn
diff --git a/net/tools/transport_security_state_generator/BUILD.gn b/net/tools/transport_security_state_generator/BUILD.gn
index 1af8b7ec26031e2265c80c19b0a261da5be2ec2d..05db192a5f2ebaf8ce5c2e1f4b15c3dea39056e7 100644
--- a/net/tools/transport_security_state_generator/BUILD.gn
+++ b/net/tools/transport_security_state_generator/BUILD.gn
@@ -4,7 +4,7 @@
 
 assert(current_toolchain == host_toolchain)
 
-executable("transport_security_state_generator") {
+source_set("transport_security_state_generator_sources") {

[Ryan Sleevi, 2017/03/30 15:03:32]

Curious: Why a source_set (and two executable targets) versus a library (and a
shared dependency)?

(I'm not sure what the 'right' pattern is, hence trying to learn more here on
the design decision)

[martijnc, 2017/03/30 19:02:22]

The GN documentation says a source_set is identical to a shared_library with the
exception that is doesn't get linked separately. This should make the build a
little faster. The lack of a linking step means that there is no dead code
elimination but I don't think that's an issue here.

"transport_security_state_generator_sources" is part of both the generator and
"transport_security_state_generator_test_sources".
"transport_security_state_generator_test_sources" gets linked into net_unittests
directly. 

   sources = [
     "bit_writer.cc",
     "bit_writer.h",
@@ -22,7 +22,6 @@ executable("transport_security_state_generator") {
     "spki_hash.h",
     "transport_security_state_entry.cc",
     "transport_security_state_entry.h",
-    "transport_security_state_generator.cc",
     "trie/trie_bit_buffer.cc",
     "trie/trie_bit_buffer.h",
     "trie/trie_writer.cc",
@@ -30,6 +29,34 @@ executable("transport_security_state_generator") {
   ]
   deps = [
     "//base",
+    "//third_party/boringssl",
+  ]
+}
+
+source_set("transport_security_state_generator_test_sources") {
+  testonly = true
+  sources = [
+    "bit_writer_unittest.cc",

[martijnc, 2017/03/26 18:53:16]

A follow-up CL will add 2 additional files here.

+    "huffman/huffman_builder_unittest.cc",
+    "spki_hash_unittest.cc",
+    "trie/trie_bit_buffer_unittest.cc",
+  ]
+  deps = [
+    ":transport_security_state_generator_sources",
+    "//base",
+    "//base/test:test_support",
+    "//testing/gmock",
+    "//testing/gtest",
+  ]
+}
+
+executable("transport_security_state_generator") {
+  sources = [
+    "transport_security_state_generator.cc",
+  ]
+  deps = [
+    ":transport_security_state_generator_sources",
+    "//base",
     "//crypto",
     "//third_party/boringssl",
   ]