Rename extension_manifest_keys namespace to extensions::manifest_keys.

chrome/common/extensions/manifest.cc

Index: chrome/common/extensions/manifest.cc
diff --git a/chrome/common/extensions/manifest.cc b/chrome/common/extensions/manifest.cc
index 008912a9571b762b0558d6dd67471a0666fb6308..f25b6d299a2c6f1927f92687620ea86de731a4a8 100644
--- a/chrome/common/extensions/manifest.cc
+++ b/chrome/common/extensions/manifest.cc
@@ -10,17 +10,16 @@
 #include "base/strings/string_split.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
-#include "chrome/common/extensions/extension_manifest_constants.h"
 #include "chrome/common/extensions/features/feature.h"
 #include "extensions/common/error_utils.h"
 #include "extensions/common/features/feature_provider.h"
 #include "extensions/common/install_warning.h"
-
-namespace errors = extension_manifest_errors;
-namespace keys = extension_manifest_keys;
+#include "extensions/common/manifest_constants.h"
 
 namespace extensions {
 
+namespace keys = manifest_keys;
+
 namespace {
 
 // Rank extension locations in a way that allows
@@ -131,10 +130,6 @@ bool Manifest::ValidateManifest(
     std::string* error,
     std::vector<InstallWarning>* warnings) const {
   *error = "";
-  if (type_ == Manifest::TYPE_PLATFORM_APP && GetManifestVersion() < 2) {
-    *error = errors::kPlatformAppNeedsManifestVersion2;
-    return false;
-  }
 
   // Check every feature to see if its in the manifest. Note that this means
   // we will ignore keys that are not features; we do this for forward