[iOS/GN] Fix compilation of ios_chrome_unittests with gn.

Get GN in sync with gyp by adding missing dependencies, removing
the obsoletes dependencies and adding missing files and targets.

Change the toolchain when targetting iOS devices to not build fat
binaries as this break the "gn gen"-time selection of the level of
optimisation to use from skia and libwebp. Instead, building for
devices on iOS is now similar to other platforms (i.e. the arch is
selected via "target_cpu" with "arm" an alias for "armv7").

Fixes the following errors:
  Undefined symbols for architecture arm64:
    "_VP8DspInitNEON", referenced from:
        _VP8DspInit in dec.o
  ...

BUG=459705,596237

Review URL: https://codereview.chromium.org/1810423002

Cr-Commit-Position: refs/heads/master@{#383416}

1 files changed, 3 insertions, 3 deletions

diff --git a/BUILD.gn b/BUILD.gn
index 35133fd..73d151a 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -197,9 +197,9 @@ group("both_gn_and_gyp") {
     ]
   } else {
     deps += [
-      #"//ios/chrome:ios_chrome_unittests", TODO(GYP)
-      #"//ios/chrome/app", TODO(GYP)
-      #"//ios/chrome/browser", TODO(GYP)
+      "//ios/chrome:ios_chrome_unittests",
+      "//ios/chrome/app",
+      "//ios/chrome/browser",
       "//ios/chrome/common",
       "//ios/net:ios_net_unittests",
       "//ios/public/provider/chrome/browser",