Revert of Disable failing GPU tests on Nexus 6.

tools/dm_flags.py

Index: tools/dm_flags.py
diff --git a/tools/dm_flags.py b/tools/dm_flags.py
index 9ab6fe9a4406deca7f8cf0f71eb8b6dfaf24188f..ea657f8e6c43fda33f061478bc3602249f53646e 100755
--- a/tools/dm_flags.py
+++ b/tools/dm_flags.py
@@ -140,11 +140,6 @@
     blacklist.extend('gpu image subset _ msaa image subset _'.split(' '))
     blacklist.extend('msaa16 gm _ tilemodesProcess'.split(' '))
 
-  # Disabled until skbug.com/3942 is resolved.
-  if 'Nexus6' in bot:
-    blacklist.extend('_ tests _ WritePixels'.split(' '))
-    blacklist.extend('_ tests _ FloatingPointTextureTest'.split(' '))
-
   if blacklist:
     args.append('--blacklist')
     args.extend(blacklist)
@@ -185,7 +180,6 @@
     'Test-Android-GCC-Nexus9-GPU-TegraK1-Arm64-Debug',
     'Test-Android-GCC-GalaxyS3-GPU-Mali400-Arm7-Debug',
     'Test-Android-GCC-GalaxyS4-GPU-SGX544-Arm7-Release',
-    'Test-Android-GCC-Nexus6-GPU-Adreno420-Arm7-Debug',
     'Test-Android-GCC-Nexus7-GPU-Tegra3-Arm7-Release',
     'Test-Android-GCC-NexusPlayer-CPU-SSSE3-x86-Release',
     'Test-Ubuntu-GCC-ShuttleA-GPU-GTX550Ti-x86_64-Release-Valgrind',