Implement `gn analyze`.

tools/gn/BUILD.gn

Index: tools/gn/BUILD.gn
diff --git a/tools/gn/BUILD.gn b/tools/gn/BUILD.gn
index e3a21ff4dd0f7ade237b20ae64f1c075615b78dd..34a2edf7e6fb06c41885c9dac91f03384afada6b 100644
--- a/tools/gn/BUILD.gn
+++ b/tools/gn/BUILD.gn
@@ -32,6 +32,7 @@ static_library("gn_lib") {
     "bundle_file_rule.h",
     "c_include_iterator.cc",
     "c_include_iterator.h",
+    "command_analyze.cc",
     "command_args.cc",
     "command_check.cc",
     "command_clean.cc",
@@ -87,6 +88,8 @@ static_library("gn_lib") {
     "functions.cc",
     "functions.h",
     "functions_target.cc",
+    "graph.cc",
+    "graph.h",
     "group_target_generator.cc",
     "group_target_generator.h",
     "header_checker.cc",
@@ -294,6 +297,7 @@ test("gn_unittests") {
     "function_write_file_unittest.cc",
     "functions_target_unittest.cc",
     "functions_unittest.cc",
+    "graph_unittest.cc",
     "header_checker_unittest.cc",
     "inherited_libraries_unittest.cc",
     "input_conversion_unittest.cc",