Fix the new Mojo EDK's mojo_system_unittests to pass in release builds and also on Linux.

mojo/edk/embedder/simple_platform_shared_buffer_unittest.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "mojo/edk/embedder/simple_platform_shared_buffer.h"
 
 #include <limits>
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 116 matching lines @@
   EXPECT_FALSE(buffer->Map(50, 51));
   EXPECT_FALSE(buffer->IsValidMap(50, 51));
   EXPECT_FALSE(buffer->Map(51, 50));
   EXPECT_FALSE(buffer->IsValidMap(51, 50));
 }
 
 TEST(SimplePlatformSharedBufferTest, TooBig) {
   // If |size_t| is 32-bit, it's quite possible/likely that |Create()| succeeds
   // (since it only involves creating a 4 GB file).
   size_t max_size = std::numeric_limits<size_t>::max();
-  if (max_size > static_cast<size_t>(base::SysInfo::AmountOfVirtualMemory()))
+  if (base::SysInfo::AmountOfVirtualMemory() &&

[jam, 2015/12/03 03:42:36]

I added this recently to make the test pass on Windows XP, but didn't test it on
Linux after. Apparently this returns 0 on Linux.

[yzshen1, 2015/12/03 18:04:33]

nit: please consider adding the reason as a comment in the code.

+      max_size > static_cast<size_t>(base::SysInfo::AmountOfVirtualMemory()))
     max_size = static_cast<size_t>(base::SysInfo::AmountOfVirtualMemory());
   scoped_refptr<SimplePlatformSharedBuffer> buffer(
       SimplePlatformSharedBuffer::Create(max_size));
   // But, assuming |sizeof(size_t) == sizeof(void*)|, mapping all of it should
   // always fail.
   if (buffer)
     EXPECT_FALSE(buffer->Map(0, max_size));
 }
 
 // Tests that separate mappings get distinct addresses.
@@ skipping 37 matching lines @@
 
   EXPECT_EQ('x', static_cast<char*>(mapping2->GetBase())[0]);
 
   static_cast<char*>(mapping2->GetBase())[1] = 'y';
   EXPECT_EQ('y', static_cast<char*>(mapping1->GetBase())[51]);
 }
 
 }  // namespace
 }  // namespace edk
 }  // namespace mojo