WebVR: Add explicit precision to all shaders to avoid Mali GPU crash

chrome/browser/android/vr_shell/mailbox_to_surface_bridge.cc

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/android/vr_shell/mailbox_to_surface_bridge.h"
 
 #include <string>
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
@@ skipping 12 matching lines @@
 
 #include <android/native_window_jni.h>
 
 #define VOID_OFFSET(x) reinterpret_cast<void*>(x)
 #define SHADER(Src) #Src
 
 namespace {
 
 /* clang-format off */
 const char kQuadCopyVertex[] = SHADER(
+    precision mediump float;
     attribute vec4 a_Position;
     attribute vec2 a_TexCoordinate;
-    varying vec2 v_TexCoordinate;
+    varying highp vec2 v_TexCoordinate;
     void main() {
       v_TexCoordinate = a_TexCoordinate;
       gl_Position = a_Position;
     }
 );
 
 const char kQuadCopyFragment[] = SHADER(
     precision highp float;
     uniform sampler2D u_Texture;
     varying vec2 v_TexCoordinate;
@@ skipping 291 matching lines @@
   // GL_NEAREST.
   gl_->BindTexture(GL_TEXTURE_2D, texture_handle);
   gl_->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
   gl_->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
   gl_->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
   gl_->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
   gl_->DrawArrays(GL_TRIANGLE_FAN, 0, 4);
 }
 
 }  // namespace vr_shell