Use google.api instead of custom googleapi package

Use the standard google.api package to not create conflicts with other
proto definition that uses the same package.

Change-Id: I264db977a2316ced0fdfb6ab8e499a1258726cb7
diff --git a/protoc_plugins/gw_gen.py b/protoc_plugins/gw_gen.py
index c63d776..6b8598d 100755
--- a/protoc_plugins/gw_gen.py
+++ b/protoc_plugins/gw_gen.py
@@ -23,7 +23,7 @@
 from jinja2 import Template
 from simplejson import dumps
 
-from chameleon.protos import annotations_pb2, http_pb2
+from google.api import annotations_pb2, http_pb2
 
 template = Template("""
 # Generated file; please do not edit
@@ -109,7 +109,7 @@
             options = method.options
             assert isinstance(options, MethodOptions)
             for fd, http in options.ListFields():
-                if fd.full_name == 'googleapi.http':
+                if fd.full_name == 'google.api.http':
                     assert fd.name == 'http'
                     assert isinstance(http, http_pb2.HttpRule)