Move test runner component into its own namespace

[email protected]
BUG=478250

Review URL: https://codereview.chromium.org/1163593006

Cr-Commit-Position: refs/heads/master@{#332598}
diff --git a/components/test_runner/web_ax_object_proxy.cc b/components/test_runner/web_ax_object_proxy.cc
index 1dfa564..ae12816 100644
--- a/components/test_runner/web_ax_object_proxy.cc
+++ b/components/test_runner/web_ax_object_proxy.cc
@@ -12,7 +12,7 @@
 #include "third_party/WebKit/public/web/WebFrame.h"
 #include "third_party/WebKit/public/web/WebKit.h"
 
-namespace content {
+namespace test_runner {
 
 namespace {
 
@@ -1335,4 +1335,4 @@
   return handle;
 }
 
-}  // namespace content
+}  // namespace test_runner