Headless: re-enable previously flaky tests

Bug: 1036627, 1036627, 1034954
TBR=gab@chromium.org, fdegans@chromium.org

This re-enables multiple headless tests suppressed after https://crrev.com/c/1977741
following the latter being reverted.

Change-Id: I074e9ba1c5fa752a0773301dc3881d3a34662cfa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1982762
Commit-Queue: Andrey Kosyakov <caseq@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#727512}

headless/lib/headless_devtools_client_browsertest.cc

@@ -668,8 +668,7 @@ class DevToolsNetworkOfflineEmulationTest
   }
 };
 
-// Flaky. https://crbug.com/1037652
-DISABLED_HEADLESS_ASYNC_DEVTOOLED_TEST_F(DevToolsNetworkOfflineEmulationTest);
+HEADLESS_ASYNC_DEVTOOLED_TEST_F(DevToolsNetworkOfflineEmulationTest);
 
 class RawDevtoolsProtocolTest
     : public HeadlessAsyncDevTooledBrowserTest,

headless/lib/headless_web_contents_browsertest.cc

@@ -255,14 +255,8 @@ class HeadlessWebContentsScreenshotWindowPositionTest
   }
 };
 
-#if defined(OS_LINUX) || defined(OS_WIN)
-// Flaky on Win/Linux: crbug.com/1036627
-DISABLED_HEADLESS_ASYNC_DEVTOOLED_TEST_P(
-    HeadlessWebContentsScreenshotWindowPositionTest);
-#else
 HEADLESS_ASYNC_DEVTOOLED_TEST_P(
     HeadlessWebContentsScreenshotWindowPositionTest);
-#endif
 
 // Instantiate test case for both software and gpu compositing modes.
 INSTANTIATE_TEST_SUITE_P(HeadlessWebContentsScreenshotWindowPositionTests,
@@ -472,13 +466,7 @@ class HeadlessWebContentsPDFPageSizeRoundingTest
   }
 };
 
-#if defined(OS_WIN) || defined(OS_LINUX)
-// Flaky on Win/Linux: crbug.com/1036627
-DISABLED_HEADLESS_ASYNC_DEVTOOLED_TEST_F(
-    HeadlessWebContentsPDFPageSizeRoundingTest);
-#else
 HEADLESS_ASYNC_DEVTOOLED_TEST_F(HeadlessWebContentsPDFPageSizeRoundingTest);
-#endif
 
 #endif  // BUILDFLAG(ENABLE_PRINTING)
 
@@ -976,12 +964,7 @@ class DontBlockWebContentsOpenTest : public WebContentsOpenTest {
   }
 };
 
-#if defined(OS_WIN) || defined(OS_LINUX)
-// Flaky on Win/Linux: crbug.com/1036627
-DISABLED_HEADLESS_ASYNC_DEVTOOLED_TEST_F(DontBlockWebContentsOpenTest);
-#else
 HEADLESS_ASYNC_DEVTOOLED_TEST_F(DontBlockWebContentsOpenTest);
-#endif
 
 class BlockWebContentsOpenTest : public WebContentsOpenTest {
  public: