Remove predefined precision qualifiers from ESSL3 samplers

New sampler types in ESSL3 should not have default precision qualifiers.
This is specified in ESSL 3.00.4 section 4.5.4.

BUG=angleproject:1222
TEST=angle_unittests

Change-Id: I9c8e7a5fbb4278db80de79bcaeebaf23e64242a0
Reviewed-on: https://chromium-review.googlesource.com/312048
Tryjob-Request: Olli Etuaho <oetuaho@nvidia.com>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
diff --git a/src/tests/gl_tests/MipmapTest.cpp b/src/tests/gl_tests/MipmapTest.cpp
index 9f4a496..281f2fb 100644
--- a/src/tests/gl_tests/MipmapTest.cpp
+++ b/src/tests/gl_tests/MipmapTest.cpp
@@ -265,7 +265,7 @@
         const std::string fragmentShaderSourceArray = SHADER_SOURCE
         (   #version 300 es\n
             precision highp float;
-            uniform sampler2DArray tex;
+            uniform highp sampler2DArray tex;
             uniform int slice;
             in vec2 texcoord;
             out vec4 out_FragColor;
@@ -303,7 +303,7 @@
         const std::string fragmentShaderSource3D = SHADER_SOURCE
         (   #version 300 es\n
             precision highp float;
-            uniform sampler3D tex;
+            uniform highp sampler3D tex;
             uniform float slice;
             uniform float lod;
             in vec2 texcoord;