Add gyp flag to specify whether we should optimize JNI generation.

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 1131 matching lines @@
         'android_sdk_tools%': '<(android_sdk_root)/platform-tools',
         'android_sdk%': '<(android_sdk_root)/platforms/android-<(android_sdk_version)',
 
         # Location of the "strip" binary, used by both gyp and scripts.
         'android_strip%' : '<!(/bin/echo -n <(android_toolchain)/*-strip)',
 
         # Provides an absolute path to PRODUCT_DIR (e.g. out/Release). Used
         # to specify the output directory for Ant in the Android build.
         'ant_build_out': '`cd <(PRODUCT_DIR) && pwd -P`',
 
+        # Determines whether we should optimize JNI generation at the cost of
+        # breaking assumptions in the build system that when inputs have changed
+        # the outputs should always change as well.  This is meant purely for
+        # developer builds, to avoid spurious re-linking of native files.
+        'optimize_jni_generation%': 0,
+
         # Always uses openssl.
         'use_openssl%': 1,
 
         'proprietary_codecs%': '<(proprietary_codecs)',
         'enable_task_manager%': 0,
         'safe_browsing%': 2,
         'configuration_policy%': 0,
         'input_speech%': 0,
         'enable_automation%': 0,
         'java_bridge%': 1,
@@ skipping 2884 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',
   },
 }