Split protoc into library and executable.

third_party/protobuf/BUILD.gn

Index: third_party/protobuf/BUILD.gn
diff --git a/third_party/protobuf/BUILD.gn b/third_party/protobuf/BUILD.gn
index e4520ec1473d5eb090d1ac311fa489f7938a2154..99bb5ffb56ef68f8bb9df26ab0bfde2c3b254a7c 100644
--- a/third_party/protobuf/BUILD.gn
+++ b/third_party/protobuf/BUILD.gn
@@ -329,7 +329,7 @@ source_set("protobuf_full") {
 
 # Only compile the compiler for the host architecture.
 if (current_toolchain == host_toolchain) {
-  executable("protoc") {
+  source_set("protoc_lib") {
     sources = [
       "src/google/protobuf/compiler/code_generator.cc",
       "src/google/protobuf/compiler/code_generator.h",
@@ -476,7 +476,6 @@ if (current_toolchain == host_toolchain) {
       "src/google/protobuf/compiler/javanano/javanano_primitive_field.h",
       "src/google/protobuf/compiler/js/js_generator.cc",
       "src/google/protobuf/compiler/js/js_generator.h",
-      "src/google/protobuf/compiler/main.cc",
       "src/google/protobuf/compiler/objectivec/objectivec_enum.cc",
       "src/google/protobuf/compiler/objectivec/objectivec_enum.h",
       "src/google/protobuf/compiler/objectivec/objectivec_enum_field.cc",
@@ -528,16 +527,32 @@ if (current_toolchain == host_toolchain) {
       configs -= [ "//build/config/win:lean_and_mean" ]
     }
 
+    public_configs = [ ":protobuf_config" ]
+
+    cflags = protobuf_lite_cflags
+
+    deps = [
+      ":protobuf_full",
+    ]
+  }
+
+  executable("protoc") {
+    sources = [
+      "src/google/protobuf/compiler/main.cc",
+    ]
+
+    configs -= [ "//build/config/compiler:chromium_code" ]
+    configs += ["//build/config/compiler:no_chromium_code"]
+
     cflags = protobuf_lite_cflags
 
     deps = [
       ":protobuf_full",

[Peter Kasting, 2016/04/28 00:29:36]

If this needs to depend on protobuf_full because anything that depends on
protoc_lib needs to depend on that, there's some syntax you should use instead
in the protoc_lib definition that basically says "treat protobuf_full as a
dependency of anything that depends on me".  I don't remember what this syntax
is, though.

[xyzzyz, 2016/04/28 20:00:31]

I think it's "public_deps". Setting this for protoc_lib.

-      "//build/config/sanitizers:deps",
+      ":protoc_lib",
 
       # Default manifest on Windows (a no-op elsewhere).
       "//build/win:default_exe_manifest",
     ]
-    deps += [ "//build/config/sanitizers:deps" ]
   }
 }