Re-add the code to only add sse2 flags on Chromium builds. It

build/common.gypi

 # Copyright (c) 2009 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'variables': {
     # .gyp files should set chromium_code to 1 if they build Chromium-specific
     # code, as opposed to external code.  This variable is used to control
     # such things as the set of warnings to enable, and whether warnings are
     # treated as errors.
@@ skipping 310 matching lines @@
             # to its original precision) but they have significant runtime
             # performance penalty.
             #
             # -mfpmath=sse -msse2 makes the compiler use SSE instructions
             # which keep floating-point values in SSE registers in its
             # native precision (32-bit for single precision, and 64-bit for
             # double precision values). This means the floating-point value
             # used during computation does not change depending on how the
             # compiler optimized the code, since the value is always kept
             # in its specified precision.
+            'conditions': [
+              ['branding=="Chromium"', {
+                'cflags': [
+                  '-march=pentium4',
+                  '-msse2',
+                  '-mfpmath=sse',
+                ],
+              }],
+            ],
             'cflags': [
               '-m32',
-              '-march=pentium4',
               '-fno-exceptions',
-              '-msse2',
-              '-mfpmath=sse',
               '-Wall',
             ],
             'ldflags': [
               '-m32',
             ],
           }],
         ],
       },
     }],
     ['OS=="mac"', {
@@ skipping 144 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }