Finish basic timer query support in GL backend

EXT_disjoint_timer_query is feature complete with the WebGL tests passing
with Chromium using ANGLE as a backend. There is some flakiness in the
timestamp query test on WebGL, but investigation revealed a bug on
Chromium's end and a fix is being made there. Since the extension is
feature complete, it is now enabled by default on OpenGL so that it can be
regression tested.

BUG=angleproject:1265

Change-Id: If018b7e3ae84aff7e40c73ff8e672a86689ae6c4
Reviewed-on: https://chromium-review.googlesource.com/324580
Tryjob-Request: Ian Ewell <ewell@google.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Ian Ewell <ewell@google.com>
diff --git a/src/libANGLE/Context.cpp b/src/libANGLE/Context.cpp
index b835c1a..8693c6f 100644
--- a/src/libANGLE/Context.cpp
+++ b/src/libANGLE/Context.cpp
@@ -1065,6 +1065,11 @@
           *params = mExtensions.maxLabelLength;
           break;
 
+      // GL_EXT_disjoint_timer_query
+      case GL_GPU_DISJOINT_EXT:
+          *params = mRenderer->getGPUDisjoint();
+          break;
+
       default:
         mState.getIntegerv(getData(), pname, params);
         break;
@@ -1092,6 +1097,11 @@
       case GL_MAX_SERVER_WAIT_TIMEOUT:
         *params = mCaps.maxServerWaitTimeout;
         break;
+
+      // GL_EXT_disjoint_timer_query
+      case GL_TIMESTAMP_EXT:
+          *params = mRenderer->getTimestamp();
+          break;
       default:
         UNREACHABLE();
         break;
@@ -1312,6 +1322,22 @@
         *type = GL_FLOAT;
         *numParams = 1;
         return true;
+      case GL_TIMESTAMP_EXT:
+          if (!mExtensions.disjointTimerQuery)
+          {
+              return false;
+          }
+          *type      = GL_INT_64_ANGLEX;
+          *numParams = 1;
+          return true;
+      case GL_GPU_DISJOINT_EXT:
+          if (!mExtensions.disjointTimerQuery)
+          {
+              return false;
+          }
+          *type      = GL_INT;
+          *numParams = 1;
+          return true;
     }
 
     if (mExtensions.debug)