Add a go-fast button to Skia GYP configs.

Add a go-fast button to Skia GYP configs.

./gyp_skia -Dskia_fast=1 will
  - always optimize for the current machine as much as possible
  - drop the frame pointer
  - optimize floating point arithmetic ignoring IEEE compliance

This allows things like 3-argument VEX prefix SSE instructions and
NEON autovectorization, and can give some seriously helpful clues
about how to rearrange floating point math for speed.

I've been having trouble with LTO linking, so I'll leave that out for now.

I don't think we should set up bots with this mode.  -ffast-math means
I'm forced to run DM with --match ~Blend ~Path ~Rect ~Math ~Scalar
~Matrix ~Point before it passes, which is a disconcerting chunk of tests
to disable (including all of PathOps).

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/dee3df930b83751577d5a3489d402c0c9e284495

[mtklein_C, 2015-03-25 14:29:02]

mtklein@chromium.org changed reviewers:
+ reed@google.com

[mtklein, 2015-03-26 12:21:27]

mtklein@google.com changed reviewers:
+ mtklein@google.com

[mtklein, 2015-03-26 12:21:27]

The CQ bit was checked by mtklein@google.com

[mtklein, 2015-03-26 12:21:27]

lgtm

[commit-bot: I haz the power, 2015-03-26 12:21:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1036533003/1

[commit-bot: I haz the power, 2015-03-26 12:21:35]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-03-26 12:21:36]

Failed to apply patch for gyp/common_conditions.gypi:
While running git apply --index -3 -p1;
  error: patch failed: gyp/common_conditions.gypi:1
  Falling back to three-way merge...
  Applied patch to 'gyp/common_conditions.gypi' with conflicts.
  U gyp/common_conditions.gypi

Patch:       gyp/common_conditions.gypi
Index: gyp/common_conditions.gypi
diff --git a/gyp/common_conditions.gypi b/gyp/common_conditions.gypi
index
fe0243d1ac3b2f236ea94294cb3732577425d6c2..cf9a1f082630c1bd7490e53bdb1f3a6cc07f42dc
100644
--- a/gyp/common_conditions.gypi
+++ b/gyp/common_conditions.gypi
@@ -1,3 +1,8 @@
+# Copyright 2015 Google Inc.
+#
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
 # conditions used in both common.gypi and skia.gyp in chromium
 #
 {
@@ -225,6 +230,7 @@
           '-Wno-invalid-offsetof',  # GCC <4.6 is old-school strict about what
is POD.
         ],
         'conditions': [
+          [ 'skia_fast', { 'cflags': [ '<@(skia_fast_flags)' ] }],
           [ 'skia_os != "chromeos"', {
             'conditions': [
               [ 'skia_arch_type == "x86_64" and not skia_android_framework', {
@@ -525,6 +531,7 @@
         },
         'xcode_settings': {
           'conditions': [
+            [ 'skia_fast', { 'WARNING_CFLAGS': [ '<@(skia_fast_flags)' ] } ],
             [ 'skia_warnings_as_errors', { 'GCC_TREAT_WARNINGS_AS_ERRORS':
'YES' }],
             [ 'skia_arch_width == 32', { 'ARCHS': ['i386']   }],
             [ 'skia_arch_width == 64', { 'ARCHS': ['x86_64'] }],

[mtklein, 2015-03-26 12:23:43]

The CQ bit was checked by mtklein@google.com

[mtklein, 2015-03-26 12:23:43]

The patchset sent to the CQ was uploaded after l-g-t-m from mtklein@google.com
Link to the patchset: https://codereview.chromium.org/1036533003/#ps20001
(title: "rebase")

[commit-bot: I haz the power, 2015-03-26 12:23:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1036533003/20001

[commit-bot: I haz the power, 2015-03-26 12:30:47]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/dee3df930b83751577d5a3489d402c0c9e284495