For iOS, don't override VALID_ARCHS in Debug configuration.

build/common.gypi

 # Copyright (c) 2012 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 4641 matching lines @@
         ['CXX.host', '<!(which g++)'],
         ['LINK.host', '<!(which g++)'],
       ],
     }],
   ],
   'configurations': {
     # DON'T ADD ANYTHING NEW TO THIS BLOCK UNLESS YOU REALLY REALLY NEED IT!
     # This block adds *project-wide* configuration settings to each project
     # file.  It's almost always wrong to put things here.  Specify your
     # custom |configurations| in target_defaults to add them to targets instead.
-    'Debug': {
-      'xcode_settings': {
-        # Enable 'Build Active Architecture Only' for Debug. This
-        # avoids a project-level warning in Xcode.
-        'ONLY_ACTIVE_ARCH': 'YES',
-      },
-    },
+    'conditions': [
+      ['OS=="ios"', {
+        'Debug': {
+          'xcode_settings': {
+            # Enable 'Build Active Architecture Only' for Debug. This
+            # avoids a project-level warning in Xcode.
+            # Note that this configuration uses the default VALID_ARCHS value
+            # because if there is a device connected Xcode sets the active arch
+            # to the arch of the device. In cases where the device's arch is not
+            # in VALID_ARCHS (e.g. iPhone5 is armv7s) Xcode complains because it
+            # can't determine what arch to compile for.
+            'ONLY_ACTIVE_ARCH': 'YES',
+          },
+        },
+        'Release': {
+          'xcode_settings': {
+            # Override VALID_ARCHS and omit armv7s. Otherwise Xcode compiles for
+            # both armv7 and armv7s, doubling the binary size.
+            'VALID_ARCHS': 'armv7 i386',

[Mark Mentovai, 2013/09/06 17:38:44]

Is this supposed to be a space-separated string instead of a list?

[lliabraa, 2013/09/06 18:12:40]

Yep

+          },
+        },
+      }],
+    ],
   },
   'xcode_settings': {
     # DON'T ADD ANYTHING NEW TO THIS BLOCK UNLESS YOU REALLY REALLY NEED IT!
     # This block adds *project-wide* configuration settings to each project
     # file.  It's almost always wrong to put things here.  Specify your
     # custom xcode_settings in target_defaults to add them to targets instead.
 
     'conditions': [
       # In an Xcode Project Info window, the "Base SDK for All Configurations"
       # setting sets the SDK on a project-wide basis. In order to get the
@@ skipping 18 matching lines @@
               }, {
                 'SDKROOT': 'iphonesimulator<(ios_sdk)',  # -isysroot
               }],
             ],
           }, {
             'SDKROOT': '<(ios_sdk_path)',  # -isysroot
           }],
         ],
       }],
       ['OS=="ios"', {
-        # Just build armv7, until armv7s is correctly tested.
-        'VALID_ARCHS': 'armv7 i386',
         # Target both iPhone and iPad.
         'TARGETED_DEVICE_FAMILY': '1,2',
       }],
       ['target_arch=="x64"', {
         'ARCHS': [
           'x86_64'
          ],
       }],
     ],
 
     # The Xcode generator will look for an xcode_settings section at the root
     # of each dict and use it to apply settings on a file-wide basis.  Most
     # settings should not be here, they should be in target-specific
     # xcode_settings sections, or better yet, should use non-Xcode-specific
     # 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',
   },
 }