Use a GN arg for controlling linker map file generation.

build/toolchain/toolchain.gni

Index: build/toolchain/toolchain.gni
diff --git a/build/toolchain/toolchain.gni b/build/toolchain/toolchain.gni
index b14928d32e7869e7bfeca1ce784bca04cba17be7..78f561867668ce3315aaff88a7ed9883f9215f0a 100644
--- a/build/toolchain/toolchain.gni
+++ b/build/toolchain/toolchain.gni
@@ -35,6 +35,16 @@ declare_args() {
   # with the build. Used on iOS to ship official builds (as they are built
   # with the version of clang shipped with Xcode).
   use_xcode_clang = is_ios && is_official_build
+
+  # Used for binary size analysis.
+  generate_linker_map = is_android && is_official_build
+}
+
+if (generate_linker_map) {
+  assert(is_official_build,
+         "Linker map files can only be generated when is_official_build = true")

[agrieve, 2017/05/17 14:33:11]

nit: can -> should

[estevenson, 2017/05/17 23:02:08]

Done.

+  assert(target_os == "android" || target_os == "linux",
+         "Linker map files can only be generated for Android and Linux")
 }
 
 # The path to the hermetic install of Xcode. Only relevant when