Revert "Disable flaky WebviewLogin Tests on ChromeOS."

This reverts commit 21168346.

Reason for revert: These tests were almost certainly fixed by the reverts in https://bugs.chromium.org/p/chromium/issues/detail?id=828529.

Original change's description:
> Disable flaky WebviewLogin Tests on ChromeOS.
> 
> Disables:
> WebviewLoginTest.StoragePartitionHandling
> WebviewProxyAuthLoginTest.ProxyAuthTransfer
> 
> Bug: 832608
> Change-Id: Ie5e2d9c8b0fd99fd3c018a004f8b7b0c567d8c38
> TBR: achuith@chromium.org
> Reviewed-on: https://chromium-review.googlesource.com/1012036
> Reviewed-by: Ramin Halavati <rhalavati@chromium.org>
> Commit-Queue: Ramin Halavati <rhalavati@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#550595}

TBR=achuith@chromium.org,rhalavati@chromium.org

Change-Id: I70215f566a19f05b8b7bea8ce867a5e47e5c417f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 832608
Reviewed-on: https://chromium-review.googlesource.com/1012757Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Commit-Queue: Alex Moshchuk <alexmos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550707}

chrome/browser/chromeos/login/webview_login_browsertest.cc

@@ -307,13 +307,7 @@ IN_PROC_BROWSER_TEST_F(WebviewLoginTest, EmailPrefill) {
   EXPECT_EQ(fake_gaia_->prefilled_email(), "user@example.com");
 }
 
-// Flaky on ChromeOS.  https://crbug.com/832608
-#if defined(OS_CHROMEOS)
-#define MAYBE_StoragePartitionHandling DISABLED_StoragePartitionHandling
-#else
-#define MAYBE_StoragePartitionHandling StoragePartitionHandling
-#endif
-IN_PROC_BROWSER_TEST_F(WebviewLoginTest, MAYBE_StoragePartitionHandling) {
+IN_PROC_BROWSER_TEST_F(WebviewLoginTest, StoragePartitionHandling) {
   WaitForGaiaPageLoad();
 
   // Start with identifer page.
@@ -944,13 +938,7 @@ class WebviewProxyAuthLoginTest : public WebviewLoginTest {
   DISALLOW_COPY_AND_ASSIGN(WebviewProxyAuthLoginTest);
 };
 
-// Flaky on ChromeOS.  https://crbug.com/832608
-#if defined(OS_CHROMEOS)
-#define MAYBE_ProxyAuthTransfer DISABLED_ProxyAuthTransfer
-#else
-#define MAYBE_ProxyAuthTransfer ProxyAuthTransfer
-#endif
-IN_PROC_BROWSER_TEST_F(WebviewProxyAuthLoginTest, MAYBE_ProxyAuthTransfer) {
+IN_PROC_BROWSER_TEST_F(WebviewProxyAuthLoginTest, ProxyAuthTransfer) {
   WaitForSigninScreen();
 
   LoginHandler* login_handler = WaitForAuthRequested();