[Extensions Cleanup] Move ExtensionBrowserTest to extensions namespace

Move the ExtensionBrowserTest class into the extensions namespace, and
updated affected sites.

This CL should have no functional change.

Bug: 117261
TBR: [email protected] (c/b/ui, c/b/autocomplete, c/b/global_keyboard_shortcuts_mac_browsertest.mm, c/b/renderer_host)
TBR: [email protected] (chrome_security_exploit_browsertest.cc)
TBR: [email protected] (c/b/chromeos)
TBR: [email protected] (c/b/metrics)
TBR: [email protected] (c/b/policy)
TBR: [email protected] (c/b/prefs)
TBR: [email protected] (c/b/printing)
TBR: [email protected] (c/b/safe_browsing)
TBR: [email protected] (c/b/site_details_browsertest.cc)
TBR: [email protected] (c/b/task_manager)
TBR: [email protected] (c/b/themes)
TBR: [email protected] (c/test/media_router)
TBR: [email protected] (c/test/ppapi)

Change-Id: I1fdbb6fc5bb94d87f40f1f02db5a91262c83c79a
Reviewed-on: https://chromium-review.googlesource.com/1050384
Reviewed-by: apacible <[email protected]>
Reviewed-by: Lei Zhang <[email protected]>
Reviewed-by: Istiaque Ahmed <[email protected]>
Commit-Queue: Devlin <[email protected]>
Cr-Commit-Position: refs/heads/master@{#557024}
diff --git a/chrome/browser/extensions/chrome_app_api_browsertest.cc b/chrome/browser/extensions/chrome_app_api_browsertest.cc
index 978739c6..fc02b55 100644
--- a/chrome/browser/extensions/chrome_app_api_browsertest.cc
+++ b/chrome/browser/extensions/chrome_app_api_browsertest.cc
@@ -25,9 +25,9 @@
 
 using extensions::Extension;
 
-class ChromeAppAPITest : public ExtensionBrowserTest {
+class ChromeAppAPITest : public extensions::ExtensionBrowserTest {
   void SetUpOnMainThread() override {
-    ExtensionBrowserTest::SetUpOnMainThread();
+    extensions::ExtensionBrowserTest::SetUpOnMainThread();
     host_resolver()->AddRule("*", "127.0.0.1");
     ASSERT_TRUE(embedded_test_server()->Start());
   }