For x64 set android_ndk_lib to /usr/lib64.

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 1503 matching lines @@
           'android_sdk_tools%': '<(android_sdk_root)/build-tools/<(android_sdk_build_tools_version)',
 
           # Android API level 14 is ICS (Android 4.0) which is the minimum
           # platform requirement for Chrome on Android, we use it for native
           # code compilation.
           'conditions': [
             ['target_arch == "ia32"', {
               'android_app_abi%': 'x86',
               'android_gdbserver%': '<(android_ndk_root)/prebuilt/android-x86/gdbserver/gdbserver',
               'android_ndk_sysroot%': '<(android_ndk_root)/platforms/android-14/arch-x86',
+              'android_ndk_lib_dir': '/usr/lib',
               'android_toolchain%': '<(android_ndk_root)/toolchains/x86-4.6/prebuilt/<(host_os)-<(android_host_arch)/bin',
             }],
             ['target_arch == "x64"', {
               'android_app_abi%': 'x86_64',
               'android_gdbserver%': '<(android_ndk_experimental_root)/prebuilt/android-x86_64/gdbserver/gdbserver',
               'android_ndk_sysroot%': '<(android_ndk_experimental_root)/platforms/android-20/arch-x86_64',
+              'android_ndk_lib_dir%': '/usr/lib64',
               'android_toolchain%': '<(android_ndk_experimental_root)/toolchains/x86_64-4.8/prebuilt/<(host_os)-<(android_host_arch)/bin',
               'android_stlport_root': '<(android_ndk_experimental_root)/sources/cxx-stl/stlport',
             }],
             ['target_arch=="arm"', {
               'conditions': [
                 ['arm_version<7', {
                   'android_app_abi%': 'armeabi',
                 }, {
                   'android_app_abi%': 'armeabi-v7a',
                 }],
               ],
               'android_gdbserver%': '<(android_ndk_root)/prebuilt/android-arm/gdbserver/gdbserver',
               'android_ndk_sysroot%': '<(android_ndk_root)/platforms/android-14/arch-arm',
+              'android_ndk_lib_dir': '/usr/lib',
               'android_toolchain%': '<(android_ndk_root)/toolchains/arm-linux-androideabi-4.6/prebuilt/<(host_os)-<(android_host_arch)/bin',
             }],
             ['target_arch == "arm64"', {
               'android_app_abi%': 'arm64-v8a',
               'android_gdbserver%': '<(android_ndk_experimental_root)/prebuilt/android-arm64/gdbserver/gdbserver',
               'android_ndk_sysroot%': '<(android_ndk_experimental_root)/platforms/android-20/arch-arm64',
+              'android_ndk_lib_dir': '/usr/lib',
               'android_toolchain%': '<(android_ndk_experimental_root)/toolchains/aarch64-linux-android-4.9/prebuilt/<(host_os)-<(android_host_arch)/bin',
               'android_stlport_root': '<(android_ndk_experimental_root)/sources/cxx-stl/stlport',
             }],
             ['target_arch == "mipsel"', {
               'android_app_abi%': 'mips',
               'android_gdbserver%': '<(android_ndk_root)/prebuilt/android-mips/gdbserver/gdbserver',
               'android_ndk_sysroot%': '<(android_ndk_root)/platforms/android-14/arch-mips',
+              'android_ndk_lib_dir': '/usr/lib',
               'android_toolchain%': '<(android_ndk_root)/toolchains/mipsel-linux-android-4.6/prebuilt/<(host_os)-<(android_host_arch)/bin',
             }],
           ],
         },
         # Copy conditionally-set variables out one scope.
         'android_app_abi%': '<(android_app_abi)',
         'android_gdbserver%': '<(android_gdbserver)',
         'android_ndk_root%': '<(android_ndk_root)',
         'android_ndk_sysroot%': '<(android_ndk_sysroot)',
         'android_sdk_root%': '<(android_sdk_root)',
         'android_sdk_version%': '<(android_sdk_version)',
         'android_toolchain%': '<(android_toolchain)',
 
         'android_ndk_include': '<(android_ndk_sysroot)/usr/include',
-        'android_ndk_lib': '<(android_ndk_sysroot)/usr/lib',
+        'android_ndk_lib': '<(android_ndk_sysroot)<(android_ndk_lib_dir)',

[rmcilroy, 2014/04/28 11:55:13]

nit - I would prefer the "/" is here (rather than in "/usr/lib") to show that
this is building a path.

         'android_sdk_tools%': '<(android_sdk_tools)',
         'android_sdk%': '<(android_sdk)',
         'android_sdk_jar%': '<(android_sdk)/android.jar',
 
         'android_stlport_root': '<(android_stlport_root)',
         'android_stlport_include': '<(android_stlport_root)/stlport',
         'android_stlport_libs_dir': '<(android_stlport_root)/libs/<(android_app_abi)',
         'host_os%': '<(host_os)',
 
         # Location of the "strip" binary, used by both gyp and scripts.
@@ skipping 3635 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',
   },
 }