Enable LTO on Linux for the official builds.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 67348d42460aba5a1b62fa69ff2fff9ec61c3bcd..23eab59c9b8b534e442f036a659eee086986ef1f 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -827,6 +827,13 @@
           'enable_prod_wallet_service%': 1,
         }],
 
+	# Enable Link Time Optimization for the official Linux Chrome.
+	# This requires LLVM Gold plugin to be downloaded.
+        # See src/tools/clang/scripts/update.py
+	['OS=="linux" and target_arch=="x64" and buildtype=="Official" and branding=="Chrome" and chromeos==0', {
+           'use_lto%': 1,
+        }],
+
         # Enable hotwording on Chrome-branded ChromeOS builds.
         ['branding=="Chrome" and chromeos==1', {
           'enable_hotwording%': 1,