Remove base::string_as_array

https://crrev.com/550137 introduced base::data(), along with a
specialization for strings to return mutable pointers. Update callers
of base::string_as_array() to use base::data() instead.

Note that this does come with an observable behaviour change:
string_as_array() returns nullptr for empty strings, while base::data()
returns the pointer to the NUL terminator (in line with std::data()).

However, this can be observed to be safe from the existing callers, due
to the preceding resizes that ensure non-empty() strings, or the
existing logic to handle empty strings.

Bug: 828324
TBR=caitkp@chromium.org, lazyboy@chromium.org, miu@chromium.org, sergeyu@chromium.org

Change-Id: I1fb5824b7115ff2b9ebf032f74a860e4cf3f52c6
Reviewed-on: https://chromium-review.googlesource.com/1056014
Commit-Queue: Ryan Sleevi <rsleevi@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558321}

• base/stl_util.h[diff]
• base/stl_util_unittest.cc[diff]
• base/trace_event/trace_event_impl.cc[diff]
• chrome/browser/extensions/install_signer.cc[diff]
• chrome/browser/media_galleries/fileapi/supported_image_type_validator.cc[diff]
• chrome/browser/plugins/plugin_power_saver_browsertest.cc[diff]
• chrome/common/component_flash_hint_file_linux.cc[diff]
• components/mirroring/browser/cast_remoting_sender.cc[diff]
• components/mirroring/service/session.cc[diff]
• components/sync/base/unique_position.cc[diff]
• content/browser/indexed_db/indexed_db_backing_store.cc[diff]
• content/renderer/media_recorder/audio_track_opus_encoder.cc[diff]
• content/renderer/media_recorder/audio_track_pcm_encoder.cc[diff]
• content/renderer/media_recorder/audio_track_recorder_unittest.cc[diff]
• crypto/sha2.cc[diff]
• extensions/browser/computed_hashes.cc[diff]
• extensions/browser/content_hash_tree.cc[diff]
• extensions/browser/content_hash_tree_unittest.cc[diff]
• extensions/browser/content_verify_job.cc[diff]
• extensions/browser/content_verify_job_unittest.cc[diff]
• extensions/browser/extension_protocols.cc[diff]
• extensions/renderer/api/display_source/wifi_display/wifi_display_audio_encoder_lpcm.cc[diff]
• media/cast/net/cast_transport_config.h[diff]
• media/cast/sender/audio_encoder.cc[diff]
• net/spdy/spdy_stream_test_util.cc[diff]
• net/websockets/websocket_basic_handshake_stream.cc[diff]
• remoting/codec/audio_decoder_opus.cc[diff]
• remoting/codec/audio_encoder_opus.cc[diff]
• remoting/codec/video_encoder_verbatim.cc[diff]
• remoting/host/file_transfer_message_handler.cc[diff]
• remoting/host/it2me/it2me_native_messaging_host_unittest.cc[diff]
• remoting/host/linux/audio_pipe_reader.cc[diff]
• remoting/host/native_messaging/native_messaging_reader.cc[diff]
• remoting/host/native_messaging/native_messaging_writer_unittest.cc[diff]
• remoting/host/security_key/security_key_message_reader.cc[diff]
• remoting/host/security_key/security_key_message_reader_impl.cc[diff]
• remoting/host/security_key/security_key_message_writer_impl_unittest.cc[diff]
• remoting/host/setup/me2me_native_messaging_host_unittest.cc[diff]
• remoting/protocol/webrtc_dummy_video_encoder.cc[diff]