Enable size_t to int truncation warnings in PPAPI

Also removed a few extra "-Wpedantic" warnings in ppapi_cpp. I don't see a good justification why this should be different than the rest of the project.

Fix GN error in media.

NOPRESUBMIT=true

Review URL: https://codereview.chromium.org/915403003

Cr-Commit-Position: refs/heads/master@{#316289}

• media/BUILD.gn[diff]
• ppapi/BUILD.gn[diff]
• ppapi/cpp/dev/file_chooser_dev.cc[diff]
• ppapi/cpp/dev/ime_input_event_dev.cc[diff]
• ppapi/cpp/dev/scriptable_object_deprecated.cc[diff]
• ppapi/cpp/dev/video_decoder_dev.cc[diff]
• ppapi/cpp/input_event.cc[diff]
• ppapi/cpp/private/content_decryptor_private.cc[diff]
• ppapi/cpp/private/flash_clipboard.cc[diff]
• ppapi/examples/gamepad/gamepad.cc[diff]
• ppapi/examples/ime/ime.cc[diff]
• ppapi/examples/printing/printing.cc[diff]
• ppapi/examples/video_decode/video_decode.cc[diff]
• ppapi/examples/video_decode/video_decode_dev.cc[diff]
• ppapi/ppapi_cpp.gypi[diff]
• ppapi/ppapi_internal.gyp[diff]
• ppapi/ppapi_tests.gypi[diff]
• ppapi/proxy/audio_input_resource.cc[diff]
• ppapi/proxy/device_enumeration_resource_helper.cc[diff]
• ppapi/proxy/file_ref_resource.cc[diff]
• ppapi/proxy/flash_clipboard_resource.cc[diff]
• ppapi/proxy/pdf_resource.cc[diff]
• ppapi/proxy/platform_verification_private_resource.cc[diff]
• ppapi/proxy/ppapi_command_buffer_proxy.cc[diff]
• ppapi/proxy/ppb_graphics_3d_proxy.cc[diff]
• ppapi/proxy/ppb_instance_proxy.cc[diff]
• ppapi/proxy/ppb_testing_proxy.cc[diff]
• ppapi/proxy/ppb_var_unittest.cc[diff]
• ppapi/proxy/ppb_video_decoder_proxy.cc[diff]
• ppapi/proxy/ppp_content_decryptor_private_proxy.cc[diff]
• ppapi/proxy/ppp_instance_proxy_unittest.cc[diff]
• ppapi/proxy/ppp_printing_proxy.cc[diff]
• ppapi/proxy/raw_var_data_unittest.cc[diff]
• ppapi/proxy/serialized_var_unittest.cc[diff]
• ppapi/proxy/url_loader_resource.cc[diff]
• ppapi/proxy/url_loader_resource.h[diff]
• ppapi/proxy/video_capture_resource.cc[diff]
• ppapi/proxy/websocket_resource.cc[diff]
• ppapi/proxy/websocket_resource_unittest.cc[diff]
• ppapi/shared_impl/array_writer.h[diff]
• ppapi/shared_impl/flash_clipboard_format_registry.cc[diff]
• ppapi/tests/test_file_io.cc[diff]
• ppapi/tests/test_file_io.h[diff]
• ppapi/tests/test_file_mapping.cc[diff]
• ppapi/tests/test_flash_clipboard.cc[diff]
• ppapi/tests/test_flash_file.cc[diff]
• ppapi/tests/test_host_resolver.cc[diff]
• ppapi/tests/test_host_resolver_private.cc[diff]
• ppapi/tests/test_memory.cc[diff]
• ppapi/tests/test_network_monitor.cc[diff]
• ppapi/tests/test_post_message.cc[diff]
• ppapi/tests/test_tcp_server_socket_private.cc[diff]
• ppapi/tests/test_tcp_socket.cc[diff]
• ppapi/tests/test_tcp_socket_private.cc[diff]
• ppapi/tests/test_udp_socket.cc[diff]
• ppapi/tests/test_udp_socket_private.cc[diff]
• ppapi/tests/test_url_loader.cc[diff]
• ppapi/tests/test_url_request.cc[diff]
• ppapi/tests/test_websocket.cc[diff]