Revert of [build] Use -O2 on linux by default (patchset #1 id:1 of...

Revert of [build] Use -O2 on linux by default (patchset #1 id:1 of https://codereview.chromium.org/1963693004/ )

Reason for revert:
Causes regressions.

Original issue's description:
> [build] Use -O2 on linux by default
>
> This switches O2 -> O3 to match chromium's configuration.
>
> This makes the difference between gn and gyp a bit smaller
> before switching.
>
> BUG=chromium:474921
> LOG=n
>
> Committed: https://crrev.com/a37ab71e343b8cc24df05868b941a49e0c271376
> Cr-Commit-Position: refs/heads/master@{#36124}

TBR=jochen@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:474921

Review-Url: https://codereview.chromium.org/1958253004
Cr-Commit-Position: refs/heads/master@{#36135}

gypfiles/toolchain.gypi

@@ -1183,13 +1183,23 @@
             'cflags!': [
               '-O0',
               '-O1',
-              '-O3',
               '-Os',
             ],
             'cflags': [
               '-fdata-sections',
               '-ffunction-sections',
-              '-O2',
+            ],
+            'conditions': [
+              # TODO(crbug.com/272548): Avoid -O3 in NaCl
+              # Don't use -O3 with sanitizers.
+              ['nacl_target_arch=="none" and asan==0 and msan==0 and lsan==0 \
+                and tsan==0 and ubsan==0 and ubsan_vptr==0', {
+                'cflags': ['-O3'],
+                'cflags!': ['-O2'],
+                }, {
+                'cflags': ['-O2'],
+                'cflags!': ['-O3'],
+              }],
             ],
           }],
           ['OS=="mac"', {
@@ -1291,14 +1301,24 @@
           ['OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="netbsd" \
             or OS=="aix"', {
             'cflags!': [
-              '-O3',
               '-Os',
             ],
             'cflags': [
               '-fdata-sections',
               '-ffunction-sections',
               '<(wno_array_bounds)',
-              '-O2',
+            ],
+            'conditions': [
+              # TODO(crbug.com/272548): Avoid -O3 in NaCl
+              # Don't use -O3 with sanitizers.
+              ['nacl_target_arch=="none" and asan==0 and msan==0 and lsan==0 \
+                and tsan==0 and ubsan==0 and ubsan_vptr==0', {
+                'cflags': ['-O3'],
+                'cflags!': ['-O2'],
+              }, {
+                'cflags': ['-O2'],
+                'cflags!': ['-O3'],
+              }],
             ],
           }],
           ['OS=="android"', {