Revert "Enable MediaSessionBrowserTest.{MultiplePlayers,Simple}PlayPause tests"

This reverts commit d89f4b46.

Reason for revert: These tests keep being flaky even after the patch
from crrev.com/c/2587045 has landed see this comment:

https://bugs.chromium.org/p/chromium/issues/detail?id=1157241#c6

Let's disable them again for now while investigating further.

Original change's description:
> Enable MediaSessionBrowserTest.{MultiplePlayers,Simple}PlayPause tests
>
> These tests were disabled due to flakiness introduced by some recent
> migrations from legacy IPC to mojo that landed past week, which I think
> should be fixed by crrev.com/c/2587045, which has been just merged.
>
> Let's re-enable them now to double-check if the fix actually worked
> as expected, keeping an eye in case they are still flaky after this.
>
> Bug: 1157263, 1157241, 1157239, 1157319
> Change-Id: I2b1daffebbb157eca5f8cce3f7692dbfabe75bf8
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2593367
> Auto-Submit: Mario Sanchez Prada <mario@igalia.com>
> Commit-Queue: Mounir Lamouri <mlamouri@chromium.org>
> Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#837643}

TBR=mlamouri@chromium.org,beccahughes@chromium.org,mario@igalia.com,chromium-scoped@luci-project-accounts.iam.gserviceaccount.com

Change-Id: Iccb8b670506aaaae9aff76e70b40d6b4a3c957db
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1157263, 1157241, 1157239, 1157319
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2595375Reviewed-by: Mario Sanchez Prada <mario@igalia.com>
Commit-Queue: Mario Sanchez Prada <mario@igalia.com>
Cr-Commit-Position: refs/heads/master@{#837696}

content/browser/media/session/media_session_browsertest.cc

@@ -247,7 +247,14 @@ IN_PROC_BROWSER_TEST_F(MediaSessionBrowserTestWithoutInternalMediaSession,
   EXPECT_TRUE(IsPlaying(shell(), "long-video"));
 }
 
-IN_PROC_BROWSER_TEST_F(MediaSessionBrowserTest, SimplePlayPause) {
+// Flaky on Linux and Android. http://crbug.com/1157239,
+// http://crbug.com/1157319
+#if defined(OS_LINUX) || defined(OS_ANDROID)
+#define MAYBE_SimplePlayPause DISABLED_SimplePlayPause
+#else
+#define MAYBE_SimplePlayPause SimplePlayPause
+#endif
+IN_PROC_BROWSER_TEST_F(MediaSessionBrowserTest, MAYBE_SimplePlayPause) {
   EXPECT_TRUE(NavigateToURL(shell(),
                             GetTestUrl("media/session", "media-session.html")));
 
@@ -265,7 +272,15 @@ IN_PROC_BROWSER_TEST_F(MediaSessionBrowserTest, SimplePlayPause) {
   EXPECT_TRUE(IsPlaying(shell(), "long-video"));
 }
 
-IN_PROC_BROWSER_TEST_F(MediaSessionBrowserTest, MultiplePlayersPlayPause) {
+// Flaky on Linux and Android. http://crbug.com/1157239,
+// http://crbug.com/1157319
+#if defined(OS_LINUX) || defined(OS_ANDROID)
+#define MAYBE_MultiplePlayersPlayPause DISABLED_MultiplePlayersPlayPause
+#else
+#define MAYBE_MultiplePlayersPlayPause MultiplePlayersPlayPause
+#endif
+IN_PROC_BROWSER_TEST_F(MediaSessionBrowserTest,
+                       MAYBE_MultiplePlayersPlayPause) {
   EXPECT_TRUE(NavigateToURL(shell(),
                             GetTestUrl("media/session", "media-session.html")));
 
@@ -317,7 +332,10 @@ IN_PROC_BROWSER_TEST_F(MediaSessionBrowserTest, MAYBE_WebContents_Muted) {
 
 #if !defined(OS_ANDROID)
 // On Android, System Audio Focus would break this test.
-IN_PROC_BROWSER_TEST_F(MediaSessionBrowserTest, MultipleTabsPlayPause) {
+
+// Flaky: http://crbug.com/1157263
+IN_PROC_BROWSER_TEST_F(MediaSessionBrowserTest,
+                       DISABLED_MultipleTabsPlayPause) {
   Shell* other_shell = CreateBrowser();
 
   EXPECT_TRUE(NavigateToURL(shell(),