Enable FIXED_POINT and -O3 for Opus when building for ARM

The original CL:
https://codereview.chromium.org/315673002/

The revert of the CL above:
https://codereview.chromium.org/349293006/

The reason for the original revert:
Media tests started failing consistently on a tsan bot
(http://build.chromium.org/p/chromium.memory.fyi/builders/Linux%20Tests%20%28tsan%29%281%29?numbuilds=200) with revision 277414 (the commit of original CL).
Cl was reverted in revision 279198.

This CL solved the problem differently, by not using the release_optimize flag, and instead replace the cflag -Os with -O3.

Opus speed gain with -03 flag on ARM:
ARM32b - 6-8% for encoding, 2% for decoding
ARM64b - 20% for encoding, 17% for decoding

Increased binary size: 

BUG=chromium:354539

Review URL: https://codereview.chromium.org/354903003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@281729 0039d316-1c4b-4281-b951-d872f2087c98

third_party/opus/opus.gyp

@@ -5,14 +5,17 @@
 {
   'variables': {
     'conditions': [
-      ['((OS=="android" or chromeos==1) and target_arch=="arm") or (OS=="ios" and target_arch=="armv7")', {
+      ['target_arch=="arm" or target_arch=="armv7" or target_arch=="arm64"', {
         'use_opus_fixed_point%': 1,
-        'use_opus_arm_optimization%': 1,
       }, {
         'use_opus_fixed_point%': 0,
+      }],
+      ['target_arch=="arm" or target_arch=="armv7"', {
+        'use_opus_arm_optimization%': 1,
+      }, {
         'use_opus_arm_optimization%': 0,
       }],
-      ['(OS=="android" or chromeos==1) and target_arch=="arm"', {
+      ['target_arch=="arm"', {
         'use_opus_rtcd%': 1,
       }, {
         'use_opus_rtcd%': 0,
@@ -56,7 +59,7 @@
             4334,  # Disable 32-bit shift warning in src/opus_encoder.c .
           ],
         }],
-        [ 'os_posix==1 and OS!="android"', {
+        ['os_posix==1 and OS!="android"', {
           # Suppress a warning given by opus_decoder.c that tells us
           # optimizations are turned off.
           'cflags': [
@@ -68,6 +71,10 @@
             ],
           },
         }],
+        ['os_posix==1 and (target_arch=="arm" or target_arch=="armv7" or target_arch=="arm64")', {
+          'cflags!': ['-Os'],
+          'cflags': ['-O3'],
+        }],
         ['use_opus_fixed_point==0', {
           'include_dirs': [
             'src/silk/float',