Roll chromium_revision 5df4e1bfe7..5bd5874cbf (518692:519731) + iOS fix

Pin iOS version to 9.0, to avoid the upstream change to 10.0

Change log: https://chromium.googlesource.com/chromium/src/+log/5df4e1bfe7..5bd5874cbf
Full diff: https://chromium.googlesource.com/chromium/src/+/5df4e1bfe7..5bd5874cbf

Changed dependencies:
* src/base: https://chromium.googlesource.com/chromium/src/base/+log/4843599735..fc034c4143
* src/build: https://chromium.googlesource.com/chromium/src/build/+log/99653454ee..f0766940d5
* src/ios: https://chromium.googlesource.com/chromium/src/ios/+log/7287c9baeb..49bd74cee7
* src/testing: https://chromium.googlesource.com/chromium/src/testing/+log/60c665fffe..373652d16f
* src/third_party: https://chromium.googlesource.com/chromium/src/third_party/+log/6a94dad699..34c5bb433a
* src/third_party/catapult: https://chromium.googlesource.com/catapult.git/+log/2ffb57b102..230a61040f
* src/third_party/depot_tools: https://chromium.googlesource.com/chromium/tools/depot_tools.git/+log/7d9d9233cb..1b30125fbc
* src/third_party/ffmpeg: https://chromium.googlesource.com/chromium/third_party/ffmpeg.git/+log/abead8cbcf..9cb03e5705
* src/third_party/icu: https://chromium.googlesource.com/chromium/deps/icu.git/+log/5ed26985c0..741688ebf3
* src/third_party/libvpx/source/libvpx: https://chromium.googlesource.com/webm/libvpx.git/+log/ea14a1a965..cbe62b9c2d
* src/tools: https://chromium.googlesource.com/chromium/src/tools/+log/4e917ad6ac..8d915c324e
DEPS diff: https://chromium.googlesource.com/chromium/src/+/5df4e1bfe7..5bd5874cbf/DEPS

No update to Clang.

TBR=marpan@webrtc.org
CQ_INCLUDE_TRYBOTS=master.internal.tryserver.corp.webrtc:linux_internal

Bug: webrtc:8570, webrtc:8580
Change-Id: I36440e0e1a3b3daac767e196acd5bfadb4eb6d9c
Reviewed-on: https://webrtc-review.googlesource.com/26026
Commit-Queue: Oleh Prypin <oprypin@webrtc.org>
Reviewed-by: Oleh Prypin <oprypin@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20919}
diff --git a/.gn b/.gn
index c3b2677..ce0cae6 100644
--- a/.gn
+++ b/.gn
@@ -62,6 +62,9 @@
 
   mac_sdk_min = "10.12"
 
+  # http://bugs.webrtc.org/8570
+  ios_deployment_target = "9.0"
+
   # WebRTC does not want to switch to C++14 yet.
   use_cxx11 = true