GN only writes files if they've changed

GN only writes files if they've changed

The write_file function should only actually update the file contents if the contents have changed to avoid unnecessary rebuilds of targets that depend on the written file.

R=thakis@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=273855

[Nico, 2014-05-29 23:33:35]

lgtm!

https://codereview.chromium.org/301973005/diff/20001/tools/gn/function_write_...
File tools/gn/function_write_file_unittest.cc (right):

https://codereview.chromium.org/301973005/diff/20001/tools/gn/function_write_...
tools/gn/function_write_file_unittest.cc:1: // Copyright 2014 The Chromium
Authors. All rights reserved.
Huh, gn isn't in a namespace gn?

https://codereview.chromium.org/301973005/diff/20001/tools/gn/function_write_...
tools/gn/function_write_file_unittest.cc:26: EXPECT_TRUE(result.type() ==
Value::NONE);  // Should always return none.
EXPECT_EQ?

https://codereview.chromium.org/301973005/diff/20001/tools/gn/function_write_...
tools/gn/function_write_file_unittest.cc:75: // Read the aacurrent time to avoid
timer resolution issues when comparing
spello aacurrent

https://codereview.chromium.org/301973005/diff/20001/tools/gn/function_write_...
tools/gn/function_write_file_unittest.cc:83: // time
candlejack'd

[brettw, 2014-05-30 00:51:49]

https://codereview.chromium.org/301973005/diff/20001/tools/gn/function_write_...
File tools/gn/function_write_file_unittest.cc (right):

https://codereview.chromium.org/301973005/diff/20001/tools/gn/function_write_...
tools/gn/function_write_file_unittest.cc:1: // Copyright 2014 The Chromium
Authors. All rights reserved.
On 2014/05/29 23:33:36, Nico (traveling) wrote:
> Huh, gn isn't in a namespace gn?

No, it's a leaf node so I don't think there's any point.

[brettw, 2014-05-30 16:24:42]

Committed patchset #3 manually as r273855 (presubmit successful).