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

build/toolchain/mac/BUILD.gn

Index: build/toolchain/mac/BUILD.gn
diff --git a/build/toolchain/mac/BUILD.gn b/build/toolchain/mac/BUILD.gn
index 423de77e4d3e355c9514a6e6a07bd936f42b9479..d19829972d4125bc26972f6ab9fd282b06a6cde6 100644
--- a/build/toolchain/mac/BUILD.gn
+++ b/build/toolchain/mac/BUILD.gn
@@ -289,7 +289,6 @@ mac_toolchain("clang_arm") {
 }
 
 mac_toolchain("ios_clang_arm") {
-  # TODO(GYP): Do we need ios_clang_armv7 and ios_clang_arm64 ?
   toolchain_cpu = "arm"
   toolchain_os = "mac"
 
@@ -303,6 +302,34 @@ mac_toolchain("ios_clang_arm") {
   is_clang = true
 }
 
+mac_toolchain("ios_clang_armv7") {
+  toolchain_cpu = "armv7"
+  toolchain_os = "mac"
+
+  # TODO(GYP): We need to support being able to use the version of clang
+  # shipped w/ XCode instead of the one pulled from upstream.
+  prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
+                       root_build_dir)
+  cc = "${goma_prefix}$prefix/clang"
+  cxx = "${goma_prefix}$prefix/clang++"
+  ld = cxx
+  is_clang = true
+}
+
+mac_toolchain("ios_clang_arm64") {
+  toolchain_cpu = "arm64"
+  toolchain_os = "mac"
+
+  # TODO(GYP): We need to support being able to use the version of clang
+  # shipped w/ XCode instead of the one pulled from upstream.
+  prefix = rebase_path("//third_party/llvm-build/Release+Asserts/bin",
+                       root_build_dir)
+  cc = "${goma_prefix}$prefix/clang"
+  cxx = "${goma_prefix}$prefix/clang++"
+  ld = cxx
+  is_clang = true
+}
+
 mac_toolchain("arm") {
   toolchain_cpu = "arm"
   toolchain_os = "mac"