Disable AppNap to avoid timeouts when running blink tests.

Layout tests do not always meet the requirements to avoid being
"napped", in which case test timeouts and other odd behavior may
occur; this is most prevalent with large repeat values and a
small number of tests.

This sets NSAppSleepDisabled to YES for blink tests.

BUG=811525
TEST=manual

Change-Id: I80ae1aeb0f5577f1977b3685e98655ea1253e3e6
Reviewed-on: https://chromium-review.googlesource.com/996483Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548438}

content/shell/app/blink_test_platform_support_mac.mm

@@ -42,6 +42,10 @@ void SetDefaultsToLayoutTestValues(void) {
              forKey:@"NSScrollAnimationEnabled"];
   [defaults setObject:@"Always"
                forKey:@"AppleShowScrollBars"];
+
+  // Disable AppNap since layout tests do not always meet the requirements to
+  // avoid "napping" which will cause test timeouts. http://crbug.com/811525.
+  [defaults setBool:YES forKey:@"NSAppSleepDisabled"];
 }
 
 }  // namespace