[1] https://cs.chromium.org/chromium/src/android_webview/browser/net/aw_network_delegate.cc?l=57&rcl=48ae0552132c3d74eaaba154120f4a68e0c27831

WIP http://crrev/c/1413692

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8824b758b35c2c44deba77d57ac468143acc61aa

commit 8824b758b35c2c44deba77d57ac468143acc61aa
Author: Nate Fischer <ntfschr@chromium.org>
Date: Thu Jan 17 02:05:45 2019

AW: apply the X-Requested-With header to all requests

No change to default code path, only network-service path.

The current code path adds the X-Requested-With header to every outgoing
request. This CL does the same for the network service code path.

This also adds tests, since this was previously uncovered. We filter out
one test for the mojo bot because loadUrl() currently doesn't work with
extra headers (which the test relies on).

R=timvolodine@chromium.org, torne@chromium.org

Bug:  922300 
Test: run_webview_instrumentation_test_apk -f AwNetworkConfigurationTest#testRequestedWith*
Change-Id: Ia9cc5f5629b7c8105d036457cbd5805120ed7e6d
Cq-Include-Trybots: master.tryserver.chromium.android:android_mojo
Reviewed-on: https://chromium-review.googlesource.com/c/1413692
Reviewed-by: Richard Coles <torne@chromium.org>
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623511}
[modify] https://crrev.com/8824b758b35c2c44deba77d57ac468143acc61aa/android_webview/browser/aw_proxying_url_loader_factory.cc
[modify] https://crrev.com/8824b758b35c2c44deba77d57ac468143acc61aa/android_webview/javatests/src/org/chromium/android_webview/test/AwContentsClientShouldInterceptRequestTest.java
[modify] https://crrev.com/8824b758b35c2c44deba77d57ac468143acc61aa/android_webview/javatests/src/org/chromium/android_webview/test/AwNetworkConfigurationTest.java
[modify] https://crrev.com/8824b758b35c2c44deba77d57ac468143acc61aa/android_webview/javatests/src/org/chromium/android_webview/test/TestAwContentsClient.java
[modify] https://crrev.com/8824b758b35c2c44deba77d57ac468143acc61aa/testing/buildbot/filters/mojo.fyi.network_webview_instrumentation_test_apk.filter

The final test should be fixed for the network service path after http://crrev/c/1415552 lands.

No manual verification necessary, we have good automated test coverage.