Remove unused IPC::Message priority.

Removes the PriorityValue enum and field from IPC::Message. This doesn't
appear to be used anywhere.

Changes the data message ctor to take a size_t data_len parameter.  This
works around an ambiguity problem with the main ctor, which has a similar
signature and would require lots of futzing with our test code to fix. To
make this work, the matching Pickle constructor is also changed to take a
size_t data_len parameter.

BUG=194304

Review URL: https://codereview.chromium.org/35643005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231330 0039d316-1c4b-4281-b951-d872f2087c98

• base/pickle.cc[diff]
• base/pickle.h[diff]
• chrome/browser/automation/chrome_frame_automation_provider_win_unittest.cc[diff]
• chrome/browser/spellchecker/spellcheck_message_filter_mac_unittest.cc[diff]
• chrome/browser/spellchecker/spellcheck_message_filter_unittest.cc[diff]
• cloud_print/service/win/service_listener.cc[diff]
• components/nacl/loader/nacl_ipc_adapter.cc[diff]
• components/nacl/loader/nacl_ipc_adapter_unittest.cc[diff]
• content/browser/renderer_host/render_view_host_unittest.cc[diff]
• content/common/cc_messages_unittest.cc[diff]
• content/common/common_param_traits_unittest.cc[diff]
• ipc/ipc_channel_posix.cc[diff]
• ipc/ipc_channel_posix_unittest.cc[diff]
• ipc/ipc_channel_unittest.cc[diff]
• ipc/ipc_channel_win.cc[diff]
• ipc/ipc_fuzzing_tests.cc[diff]
• ipc/ipc_logging.cc[diff]
• ipc/ipc_message.cc[diff]
• ipc/ipc_message.h[diff]
• ipc/ipc_message_macros.h[diff]
• ipc/ipc_message_unittest.cc[diff]
• ipc/ipc_message_utils_unittest.cc[diff]
• ipc/ipc_perftests.cc[diff]
• ipc/ipc_send_fds_test.cc[diff]
• ipc/ipc_sync_message.cc[diff]
• ipc/ipc_sync_message.h[diff]
• ppapi/host/resource_message_filter_unittest.cc[diff]
• ppapi/proxy/handle_converter.cc[diff]