Release v1.6.0 (#324)

* Update version and changelog for v1.6.0
* Update docs
diff --git a/docs/dyn/servicecontrol_v1.services.html b/docs/dyn/servicecontrol_v1.services.html
index 0fec2b9..c367090 100644
--- a/docs/dyn/servicecontrol_v1.services.html
+++ b/docs/dyn/servicecontrol_v1.services.html
@@ -79,7 +79,7 @@
 <p class="firstline">Checks an operation with Google Service Control to decide whether</p>
 <p class="toc_element">
   <code><a href="#report">report(serviceName=None, body, x__xgafv=None)</a></code></p>
-<p class="firstline">Reports operations to Google Service Control. It should be called</p>
+<p class="firstline">Reports operation results to Google Service Control, such as logs and</p>
 <h3>Method Details</h3>
 <div class="method">
     <code class="details" id="check">check(serviceName=None, body, x__xgafv=None)</code>
@@ -87,6 +87,12 @@
 the given operation should proceed. It should be called before the
 operation is executed.
 
+If feasible, the client should cache the check results and reuse them for
+60 seconds. In case of server errors, the client can rely on the cached
+results for longer time.
+
+NOTE: the `CheckRequest` has the size limit of 1MB.
+
 This method requires the `servicemanagement.services.check` permission
 on the specified service. For more information, see
 [Google Cloud IAM](https://cloud.google.com/iam).
@@ -279,6 +285,11 @@
           # and an idempotent id is desirable for deduplication purpose, UUID version 5
           # is recommended. See RFC 4122 for details.
     },
+    "serviceConfigId": "A String", # Specifies which version of service configuration should be used to process
+        # the request.
+        # 
+        # If unspecified or no matching version can be found, the
+        # latest one will be used.
   }
 
   x__xgafv: string, V1 error format.
@@ -309,8 +320,16 @@
 
 <div class="method">
     <code class="details" id="report">report(serviceName=None, body, x__xgafv=None)</code>
-  <pre>Reports operations to Google Service Control. It should be called
-after the operation is completed.
+  <pre>Reports operation results to Google Service Control, such as logs and
+metrics. It should be called after an operation is completed.
+
+If feasible, the client should aggregate reporting data for up to 5
+seconds to reduce API traffic. Limiting aggregation to 5 seconds is to
+reduce data loss during client crashes. Clients should carefully choose
+the aggregation time window to avoid data loss risk more than 0.01%
+for business and compliance reasons.
+
+NOTE: the `ReportRequest` has the size limit of 1MB.
 
 This method requires the `servicemanagement.services.report` permission
 on the specified service. For more information, see
@@ -515,6 +534,11 @@
             # is recommended. See RFC 4122 for details.
       },
     ],
+    "serviceConfigId": "A String", # Specifies which version of service config should be used to process the
+        # request.
+        # 
+        # If unspecified or no matching version can be found, the
+        # latest one will be used.
   }
 
   x__xgafv: string, V1 error format.
@@ -538,8 +562,9 @@
         #    `Operations` in the request succeeded. Each
         #    `Operation` that failed processing has a corresponding item
         #    in this list.
-        # 3. A failed RPC status indicates a complete failure where none of the
-        #    `Operations` in the request succeeded.
+        # 3. A failed RPC status indicates a general non-deterministic failure.
+        #    When this happens, it's impossible to know which of the
+        #    'Operations' in the request succeeded or failed.
       { # Represents the processing error of one `Operation` in the request.
         "status": { # The `Status` type defines a logical error model that is suitable for different # Details of the error when processing the `Operation`.
             # programming environments, including REST APIs and RPC APIs. It is used by