Move unique name generation and tracking into //content.

content/test/BUILD.gn

Index: content/test/BUILD.gn
diff --git a/content/test/BUILD.gn b/content/test/BUILD.gn
index 6a03905e0b7fc8dbe1d6c81d83e148ebb2854e38..778c0e444bccb35f9e14447219b2f9cdee4b33fd 100644
--- a/content/test/BUILD.gn
+++ b/content/test/BUILD.gn
@@ -504,6 +504,26 @@ static_library("layouttest_support") {
   }
 }
 
+static_library("test_runner_support") {
+  testonly = true
+
+  # See comment at the top of //content/BUILD.gn for why this is disabled in
+  # component builds.
+  if (is_component_build) {
+    check_includes = false
+  }
+
+  sources = [
+    "../public/test/test_runner_support.h",
+    "test_runner_support.cc",
+  ]
+
+  deps = [
+    "//content/renderer:for_content_tests",
+    "//third_party/WebKit/public:blink",
+  ]
+}
+
 if (is_android) {
   import("//build/config/android/rules.gni")