GYP: fix compile flake for second-hand use of generated headers.

mojo/public/tools/bindings/mojom_bindings_generator_explicit.gypi

 # Copyright 2013 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.
 
 {
   'includes': [
     'mojom_bindings_generator_variables.gypi',
   ],
   'variables': {
     'mojom_base_output_dir':
         '<!(python <(DEPTH)/build/inverse_depth.py <(DEPTH))',
     'mojom_generated_outputs': [
       '<!@(python <(DEPTH)/mojo/public/tools/bindings/mojom_list_outputs.py --basedir <(mojom_base_output_dir) <@(mojom_files))',
     ],
   },
+  # Given mojom files as inputs, generate sources.  These sources will be
+  # exported to another target (via dependent_settings) to be compiled.  This
+  # keeps code generation separate from compilation, allowing the same sources
+  # to be compiled with multiple toolchains - target, NaCl, etc.
   'actions': [
     {
       'action_name': '<(_target_name)_mojom_bindings_generator',
       'variables': {
         'java_out_dir': '<(PRODUCT_DIR)/java_mojo/<(_target_name)/src',
         'mojom_import_args%': [
          '-I<(DEPTH)'
         ],
       },
       'inputs': [
         '<@(mojom_bindings_generator_sources)',
         '<@(mojom_files)',
       ],
       'outputs': [
         '<@(mojom_generated_outputs)',
       ],
       'action': [
         'python', '<@(mojom_bindings_generator)',
         '<@(mojom_files)',
         '--use_chromium_bundled_pylibs',
         '-d', '<(DEPTH)',
         '<@(mojom_import_args)',
         '-o', '<(SHARED_INTERMEDIATE_DIR)',
         '--java_output_directory=<(java_out_dir)',
       ],
       'message': 'Generating Mojo bindings from <@(mojom_files)',
-      'process_outputs_as_sources': 1,
     }
   ],
   'direct_dependent_settings': {
+    # A target directly depending on this action will compile the generated
+    # sources.
     'sources': [
       '<@(mojom_generated_outputs)',
     ],
     # Include paths needed to compile the generated sources into a library.
     'include_dirs': [
       '<(DEPTH)',
       '<(SHARED_INTERMEDIATE_DIR)',
     ],
+    # Make sure the generated header files are available for any static library
+    # that depends on a static library that depends on this generator.
+    'hard_dependency': 1,
     'direct_dependent_settings': {
       # Include paths needed to find the generated header files and their
       # transitive dependancies when using the library.
       'include_dirs': [
         '<(DEPTH)',
         '<(SHARED_INTERMEDIATE_DIR)',
       ],
       'variables': {
-        'generated_src_dirs': [
-          '<(PRODUCT_DIR)/java_mojo/<(_target_name)/src',
-        ],
+        'generated_src_dirs': [
+          '<(PRODUCT_DIR)/java_mojo/<(_target_name)/src',
+        ],
       },
     }
   },
-  'hard_dependency': 1,
 }