Revert of [build] Use -O2 on linux by default

gypfiles/toolchain.gypi

Index: gypfiles/toolchain.gypi
diff --git a/gypfiles/toolchain.gypi b/gypfiles/toolchain.gypi
index bb016e72a28c402edbed71272a5284682edc2406..ee6cd20067554e4b8bdb80916765d4acabaa1875 100644
--- a/gypfiles/toolchain.gypi
+++ b/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"', {