WebContents and WebContentsObserver should not provide IPC::Sender API.

With the introduction of OOPIFs, WebContents can span multiple processes
- there is no default process to send IPC messages to.  Removing the
WebContents::Send and WebContentsObserver::Send methods forces the
callers to explicitly specify the target of the message.  This helps
avoid situations where an IPC message is sent via RenderViewHost (i.e.
to the process hosting the main frame) when it should have been send to
a process hosting a specific frame (this CL fixes a few such cases).

Bug: 663029
Change-Id: I16980f5ef05a8ac7da365edf7a92ce46677a8c0c
Reviewed-on: https://chromium-review.googlesource.com/630416
Reviewed-by: Gene Gutnik <gene@chromium.org>
Reviewed-by: Selim Gurun <sgurun@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Bernhard Bauer <bauerb@chromium.org>
Reviewed-by: Lucas Gadani <lfg@chromium.org>
Reviewed-by: Alex Clarke <alexclarke@chromium.org>
Reviewed-by: Nick Carter <nick@chromium.org>
Commit-Queue: Łukasz Anforowicz <lukasza@chromium.org>
Cr-Commit-Position: refs/heads/master@{#500170}

• android_webview/browser/aw_print_manager.cc[diff]
• android_webview/browser/aw_print_manager.h[diff]
• android_webview/browser/renderer_host/aw_render_view_host_ext.cc[diff]
• chrome/browser/android/tab_android.cc[diff]
• chrome/browser/guest_view/web_view/chrome_web_view_permission_helper_delegate.cc[diff]
• chrome/browser/plugins/plugin_observer.cc[diff]
• chrome/browser/plugins/plugin_observer.h[diff]
• chrome/browser/printing/print_view_manager.cc[diff]
• chrome/browser/printing/print_view_manager.h[diff]
• components/guest_view/browser/guest_view_base.cc[diff]
• content/browser/browser_plugin/browser_plugin_guest.cc[diff]
• content/browser/media/media_web_contents_observer.cc[diff]
• content/browser/media/session/media_session_controller.cc[diff]
• content/browser/plugin_content_origin_whitelist.cc[diff]
• content/browser/web_contents/web_contents_impl.cc[diff]
• content/browser/web_contents/web_contents_impl.h[diff]
• content/public/browser/web_contents.h[diff]
• content/public/browser/web_contents_observer.cc[diff]
• content/public/browser/web_contents_observer.h[diff]
• content/shell/browser/layout_test/blink_test_controller.cc[diff]
• extensions/browser/guest_view/extensions_guest_view_manager_delegate.cc[diff]
• headless/lib/browser/headless_print_manager.cc[diff]
• headless/lib/browser/headless_print_manager.h[diff]