Skip a few context_lost gpu integration tests on Nexus 6

In https://chromium-review.googlesource.com/c/chromium/src/+/1788138,
these tests were enabled on Android. But flakes are seen on Nexus 6:
https://ci.chromium.org/p/chromium/builders/ci/Android%20FYI%20Release%20%28Nexus%206%29/33613

Following the similar pattern of skipping them as in:
https://chromium-review.googlesource.com/c/chromium/src/+/1808584
https://chromium-review.googlesource.com/c/chromium/src/+/1628391

TBR=kbr@chromium.org

Bug: 609629
Change-Id: Icd07a38c4e3a5ff8c12c791bdf0f6b066014e726
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2401708Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Shrek Shao <shrekshao@google.com>
Cr-Commit-Position: refs/heads/master@{#805587}

content/test/gpu/gpu_tests/test_expectations/context_lost_expectations.txt

@@ -43,6 +43,9 @@ crbug.com/611906 [ android qualcomm-adreno-(tm)-420 ] ContextLost_WebGLContextLo
 crbug.com/609629 [ android qualcomm-adreno-(tm)-420 ] GpuCrash_GPUProcessCrashesExactlyOncePerVisitToAboutGpuCrash [ Skip ]
 crbug.com/609629 [ android qualcomm-adreno-(tm)-420 ] ContextLost_WebGLContextLostFromGPUProcessExit [ Skip ]
 crbug.com/609629 [ android qualcomm-adreno-(tm)-420 ] ContextLost_WebGLContextLostInHiddenTab [ Skip ]
+crbug.com/609629 [ android qualcomm-adreno-(tm)-420 ] ContextLost_WebGLBlockedAfterJSNavigation [ Skip ]
+crbug.com/609629 [ android qualcomm-adreno-(tm)-420 ] ContextLost_WebGLContextLostFromSelectElement [ Skip ]
+crbug.com/609629 [ android qualcomm-adreno-(tm)-420 ] ContextLost_WebGLUnblockedAfterUserInitiatedReload [ Skip ]
 
 # Flaking on Nexus 9
 crbug.com/609629 [ android nvidia ] ContextLost_WebGLBlockedAfterJSNavigation [ Skip ]