In CompositeHTTPBodyStream, coalesce small GetBytesBuffer()s to better fill the buffer.

util/net/http_body_test.cc

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 196 matching lines @@
 
   CompositeHTTPBodyStream stream(parts);
 
   std::string expected_string = string1 + "This is a test.\n" + string2;
   std::string actual_string = ReadStreamToString(&stream, GetParam());
   EXPECT_EQ(expected_string, actual_string);
 }
 
 INSTANTIATE_TEST_CASE_P(VariableBufferSize,
                         CompositeHTTPBodyStreamBufferSize,
-                        testing::Values(1, 2, 9, 16, 31, 128));
+                        testing::Values(1, 2, 9, 16, 31, 128, 1024));
 
 }  // namespace
 }  // namespace test
 }  // namespace crashpad