Reland: "tools: allow building merger tool on Bazel"

Add a fix for breakage when rolling into G3

This reverts commit 5bcd176623e8b3bc490761e5a35bbb952fa269b9.

Change-Id: I304a8ea6168d452380de10657fd771b7fd935a5e
Bug: 188053828

BUILD

diff --git a/BUILD b/BUILD
index 139ee59..e4cf755 100644
--- a/BUILD
+++ b/BUILD
@@ -186,6 +186,22 @@
     ] + PERFETTO_CONFIG.deps.protobuf_full,
 )
 
+# GN target: //tools/proto_merger:proto_merger
+perfetto_cc_binary(
+    name = "proto_merger",
+    srcs = [
+        "tools/proto_merger/allowlist.h",
+        "tools/proto_merger/main.cc",
+        "tools/proto_merger/proto_file.cc",
+        "tools/proto_merger/proto_file.h",
+        "tools/proto_merger/proto_merger.cc",
+        "tools/proto_merger/proto_merger.h",
+    ],
+    deps = [
+        ":src_base_base",
+    ] + PERFETTO_CONFIG.deps.protobuf_full,
+)
+
 # GN target: //:libperfetto
 perfetto_cc_library(
     name = "libperfetto",