Add a dedicated "optimize_speed" config to GN.

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 0cba95ff63396ac21889680191dd8777050cce26..481b004c6d1ac308a2a693d8f46523c42d352a79 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -1399,6 +1399,49 @@ config("optimize_max") {
   }
 }
 
+# This config can be used to override the default settings for per-component
+# and whole-program optimization, optimizing the particular target for speed
+# instead of code size. This config is exactly the same as "optimize_max"
+# except that we use -O3 instead of -O2 on non-win, non-IRT platforms.
+#
+# TODO(crbug.com/621335) - rework how all of these configs are related
+# so that we don't need this disclaimer.
+config("optimize_speed") {

[Nico, 2016/06/21 18:10:37]

bikeshed: I think it'd be good if the name contained "also, this will increase
binary size" – else people will see this and think "well speed is good i better
add this to my target!"

+  if (is_nacl_irt) {
+    # The NaCl IRT is a special case and always wants its own config.
+    # Various components do:
+    #   if (!is_debug) {
+    #     configs -= [ "//build/config/compiler:default_optimization" ]
+    #     configs += [ "//build/config/compiler:optimize_max" ]
+    #   }
+    # So this config has to have the selection logic just like
+    # "default_optimization", below.
+    configs = [ "//build/config/nacl:irt_optimize" ]
+  } else {
+    ldflags = common_optimize_on_ldflags
+    if (is_win) {
+      # Favor speed over size, /O2 must be before the common flags. The GYP
+      # build also specifies /Ot, /Oi, and /GF, but these are implied by /O2.
+      cflags = [ "/O2" ] + common_optimize_on_cflags
+
+      # TODO(thakis): Remove is_clang here, https://crbug.com/598772
+      if (is_official_build && !is_clang) {
+        cflags += [
+          "/GL",  # Whole program optimization.
+
+          # Disable Warning 4702 ("Unreachable code") for the WPO/PGO builds.
+          # Probably anything that this would catch that wouldn't be caught in a
+          # normal build isn't going to actually be a bug, so the incremental
+          # value of C4702 for PGO builds is likely very small.
+          "/wd4702",
+        ]

[Nico, 2016/06/21 18:10:37]

this is a lot of copy-pasta :-/

+      }
+    } else {
+      cflags = [ "-O3" ] + common_optimize_on_cflags
+    }
+  }
+}
+
 # The default optimization applied to all targets. This will be equivalent to
 # either "optimize" or "no_optimize", depending on the build flags.
 config("default_optimization") {