Update Linux gyp build to import and propagate external environment...

build/SConscript.main

 # Copyright (c) 2006-2008 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.
 
 import os
 import shutil
 import sys
 
 
 if sys.platform == 'win32':
@@ skipping 68 matching lines @@
     tools = tool_list,
     variables = clvars,
 
     # Requested list of system (shared) libraries, from the comma separated
     # SYSTEM_LIBS command-line argument
     req_system_libs = [],
     # All supported system libraries, for the help message
     all_system_libs = [],
 
     CHROME_SRC_DIR = '$MAIN_DIR/..',
+    SRC_DIR = '$MAIN_DIR/..',
     DESTINATION_ROOT = '$MAIN_DIR/$BUILD_TARGET_DIR',
 
     # Where ComponentTestProgram() will build test executables.
     TESTS_DIR = '$DESTINATION_ROOT',
 
     # Where ComponentProgram() will build program executables.
     STAGING_DIR = '$DESTINATION_ROOT',
 
     # TODO(hammer):  when Hammer supports this...
     # Have Hammer prefix all Library aliases with lib_ (to avoid
@@ skipping 669 matching lines @@
 
 # Overlay things from a layer below.
 for env in environment_list:
   env.Dir('$OBJ_ROOT').addRepository(env.Dir('$CHROME_SRC_DIR'))
   env.Dir('$OBJ_ROOT/googleurl').addRepository(env.Dir('$CHROME_SRC_DIR/build'))
 
   # We pre-resolve some common targets.  We end up spending lots of time
   # resolving these over and over again.
   env.Replace(
       CHROME_SRC_DIR        = str(env.Dir('$CHROME_SRC_DIR')),
+      SRC_DIR               = str(env.Dir('$SRC_DIR')),
       DESTINATION_ROOT      = str(env.Dir('$DESTINATION_ROOT')),
       TARGET_ROOT           = str(env.Dir('$TARGET_ROOT')),
       OBJ_ROOT              = str(env.Dir('$OBJ_ROOT')),
       WEBKIT_DIR            = str(env.Dir('$WEBKIT_DIR')),
   )
 
 
 help_fmt = """
 Usage: hammer [SCONS_OPTIONS] [VARIABLES] [TARGET] ...
 
@@ skipping 101 matching lines @@
         'all_libraries',
         'all_languages',
         'all_programs',
         'all_test_programs',
     ], projects = [p],
     COMPONENT_VS_PROJECT_SCRIPT_PATH=(
         'cd $$(ProjectDir)/$VS_PROJECT_TO_MAIN_DIR && hammer.bat'),
 )
 
 # -------------------------------------------------------------------------