Problems showing pdf

I have problems trying to show a pdf, in android directly it never loads them and in Ios, it depends on the server, if it is https it shows them, if it is http, it does not show them.

In apple I have no feedback.
In Android I have this the first time I run the plugin:

```
I/WebViewFactory(32731): Loading com.google.android.webview version 68.0.3440.85 (code 344008500)
I/art (32731): Rejecting re-init on previously-failed class java.lang.Class
I/art (32731): Rejecting re-init on previously-failed class java.lang.Class
I/art (32731): Rejecting re-init on previously-failed class java.lang.Class
I/art (32731): Rejecting re-init on previously-failed class java.lang.Class
I/cr_LibraryLoader(32731): Time to load native libraries: 4 ms (timestamps 3006-3010)
E/cr_VariationsUtils(32731): Failed reading seed file "/data/user/0/com.example.webviewtest/app_webview/variations_seed_new": /data/user/0/com.example.webviewtest/app_webview/variations_seed_new: open failed: ENOENT (No such file or directory)
I/chromium(32731): [INFO:library_loader_hooks.cc(36)] Chromium logging enabled: level = 0, default verbosity = 0
I/cr_LibraryLoader(32731): Expected native library version number "68.0.3440.85", actual native library version number "68.0.3440.85"
I/cr_BrowserStartup(32731): Initializing chromium process, singleProcess=true
I/cr_base (32731): Android Locale: es_US requires .pak files: []
I/chromium(32731): [INFO:aw_field_trial_creator.cc(52)] First-WebView-Experiment found, group=Enabled
I/art (32731): Rejecting re-init on previously-failed class java.lang.Class
I/art (32731): Rejecting re-init on previously-failed class java.lang.Class
I/art (32731): Rejecting re-init on previously-failed class java.lang.Class
I/art (32731): Rejecting re-init on previously-failed class java.lang.Class
E/libEGL (32731): validate_display:255 error 3008 (EGL_BAD_DISPLAY)
W/cr_media(32731): Requires BLUETOOTH permission
W/cr_CrashFileManager(32731): /data/user/0/com.example.webviewtest/cache/WebView/Crash Reports does not exist or is not a directory
W/VideoCapabilities(32731): Unrecognized profile 2130706433 for video/avc
W/VideoCapabilities(32731): Unrecognized profile/level 0/3 for video/mpeg2
W/VideoCapabilities(32731): Unrecognized profile/level 0/0 for video/mpeg2
W/VideoCapabilities(32731): Unrecognized profile/level 0/2 for video/mpeg2
W/VideoCapabilities(32731): Unrecognized profile/level 0/3 for video/mpeg2
I/VideoCapabilities(32731): Unsupported profile 4 for video/mp4v-es
```

I'm using WebviewScaffold, but I just realized that when I try to open a fullscreen or a rect, it does not do anything (android). It also does not show any error.

Pdf examples:
http://www.pdfpdf.com/samples/Sample1.PDF (not work in android or ios)
https://www.adobe.com/support/products/enterprise/knowledgecenter/media/c4611_sample_explain.pdf (only work in ios)

Tested in Iphone 6 (ios 11.4.1), and MotoG3 (android 6.0)

This is my flutter doctor.

```
[flutter] flutter doctor
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel master, v0.5.8-pre.199, on Mac OS X 10.13.6 17G65, locale en-CA)
[✓] Android toolchain - develop for Android devices (Android SDK 27.0.3)
[✓] iOS toolchain - develop for iOS devices (Xcode 9.4.1)
[✓] Android Studio (version 3.1)
[✓] VS Code (version 1.25.1)
[✓] Connected devices (2 available)
```

Bắt đầu bằng cách tái hiện các URL PDF đã được báo cáo thông qua WebviewScaffold trên các phiên bản Android và iOS được liệt kê, sau đó kiểm tra cách plugin xử lý WebView dành riêng cho từng nền tảng. Công việc được xem là hoàn tất khi các URL PDF được hỗ trợ tải nhất quán hoặc giới hạn của nền tảng được ghi lại cùng thông tin lỗi hữu ích.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.