Add unit test for glsl-construct-vec-mat-index's expectations.

tools/telemetry/telemetry/testing/fakes/__init__.py

Index: tools/telemetry/telemetry/testing/fakes/__init__.py
diff --git a/tools/telemetry/telemetry/testing/fakes/__init__.py b/tools/telemetry/telemetry/testing/fakes/__init__.py
index a28fa742487e755d9f0c8e7e1e5c1c60a499e5e2..7e4095091932c04841004efc1792b1390799b010 100644
--- a/tools/telemetry/telemetry/testing/fakes/__init__.py
+++ b/tools/telemetry/telemetry/testing/fakes/__init__.py
@@ -142,6 +142,7 @@ class _FakeBrowser(object):
     self._tabs = _FakeTabList(self)
     self._returned_system_info = FakeSystemInfo()
     self._platform = platform
+    self._browser_type = 'release'
 
   @property
   def platform(self):
@@ -167,6 +168,16 @@ class _FakeBrowser(object):
     self._returned_system_info = incoming
 
   @property
+  def browser_type(self):
+    """The browser_type this browser claims to be ('debug', 'release', etc.)"""
+    return self._browser_type
+
+  @browser_type.setter
+  def browser_type(self, incoming):
+    """Allows setting of the browser_type."""
+    self._browser_type = incoming
+
+  @property
   def credentials(self):
     return _FakeCredentials()