Fix Linux code coverage.

chrome/chrome.gyp

 # 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': {
     'chromium_code': 1,
     # Define the common dependencies that contain all the actual
     # Chromium functionality.  This list gets pulled in below by
     # the link of the actual chrome (or chromium) executable on
@@ skipping 4643 matching lines @@
           # E.g. build/{linux|mac}/chrome_linux.croc
           'dependencies': [
             '../base/base.gyp:base_unittests',
             '../media/media.gyp:media_unittests',
             '../net/net.gyp:net_unittests',
             '../printing/printing.gyp:printing_unittests',
             'unit_tests',
           ],
           'actions': [
             {
-              # 'message' for Linux/scons in particular
+              # 'message' for Linux/scons in particular.  Scons
+              # requires the 'coverage' target be run from within
+              # src/chrome.
               'message': 'Running coverage_posix.py to generate coverage numbers',
               'inputs': [],
               'outputs': [],
               'action_name': 'coverage',
               'action': [ 'python',
                           '../tools/code_coverage/coverage_posix.py',
                           '--directory',
                           '<(PRODUCT_DIR)',
                           '--',
                           '<@(_dependencies)'],
               # Use outputs of this action as inputs for the main target build.
               # Seems as a misnomer but makes this happy on Linux (scons).
               'process_outputs_as_sources': 1,
             },
           ],  # 'actions'
         },
       ]
     }],
   ],  # 'conditions'
 }