Add -pie to chrome on Linux in GN.

This matches the GYP build.

Review URL: https://codereview.chromium.org/1134833003

Cr-Commit-Position: refs/heads/master@{#329565}

chrome/BUILD.gn

@@ -116,11 +116,9 @@ if (!is_android) {
       # Needed for chrome_main.cc initialization of libraries.
       configs += [ "//build/config/linux:pangocairo" ]
 
-      # TODO(GYP) ['profiling==0 and linux_disable_pie==0', {
-      #   'ldflags': [
-      #      '-pie',
-      #   ],
-      #}],
+      # GYP has this in a 'profiling==0 and linux_disable_pie==0' condition.
+      # but GN doesn't have either of these flags.
+      ldflags = [ "-pie" ]
 
       if (use_x11) {
         configs += [