base: Remove const modifier from return type of DiscardableMemory::data_as().

To allow this helper function to also be used for writing to
discardable memory region.

BUG=

Review URL: https://codereview.chromium.org/1100463002

Cr-Commit-Position: refs/heads/master@{#326362}
diff --git a/base/memory/discardable_memory.h b/base/memory/discardable_memory.h
index 4138684..fc189e746 100644
--- a/base/memory/discardable_memory.h
+++ b/base/memory/discardable_memory.h
@@ -56,8 +56,8 @@
   virtual void* data() const = 0;
 
   // Handy method to simplify calling data() with a reinterpret_cast.
-  template<typename T> const T* data_as() const {
-    return reinterpret_cast<const T*>(data());
+  template<typename T> T* data_as() const {
+    return reinterpret_cast<T*>(data());
   }
 };