[testsharder] Add CPU as a dimension

Needed, for example, for linux tests to target the appropriate cpu
type.

Change-Id: Ie5877bc32c2758bb6e6d8ce67f2727e824e6f17c
diff --git a/testsharder/environment.go b/testsharder/environment.go
index 80ccba1..d0b2226 100644
--- a/testsharder/environment.go
+++ b/testsharder/environment.go
@@ -45,6 +45,9 @@
 
 	// The OS to run the test on (e.g., "Linux" or "Mac"). Used for host-side testing.
 	OS string `json:"os,omitempty"`
+
+	// The CPU type that the test is meant to run on.
+	CPU string `json:"cpu,omitempty"`
 }
 
 // ResolvesTo gives a partial ordering on DimensionSets in which one resolves to