Fix google-build-using-namespace warnings in cpu_ref.

* Remove "using namespace ..." statements.
* Replace them with using declarations of the required names.
* Enclose the C++ methods and static and extern "C" functions with
  namespace android and renderscript.
* Keep global C++ functions as-is and add using declarations for them.

Bug: 32670901
Test: build with WITH_TIDY=1
Change-Id: I818de466e8786a6c4f9ce0cd8e0fe027f34d7fad
diff --git a/cpu_ref/rsCpuIntrinsicHistogram.cpp b/cpu_ref/rsCpuIntrinsicHistogram.cpp
index 88d991b..f3b7146 100644
--- a/cpu_ref/rsCpuIntrinsicHistogram.cpp
+++ b/cpu_ref/rsCpuIntrinsicHistogram.cpp
@@ -17,9 +17,6 @@
 #include "rsCpuIntrinsic.h"
 #include "rsCpuIntrinsicInlines.h"
 
-using namespace android;
-using namespace android::renderscript;
-
 namespace android {
 namespace renderscript {
 
@@ -77,9 +74,6 @@
 
 };
 
-}
-}
-
 void RsdCpuScriptIntrinsicHistogram::setGlobalObj(uint32_t slot, ObjectBase *data) {
     rsAssert(slot == 1);
     mAllocOut.set(static_cast<Allocation *>(data));
@@ -324,8 +318,10 @@
 void RsdCpuScriptIntrinsicHistogram::invokeFreeChildren() {
 }
 
-
 RsdCpuScriptImpl * rsdIntrinsic_Histogram(RsdCpuReferenceImpl *ctx, const Script *s, const Element *e) {
 
     return new RsdCpuScriptIntrinsicHistogram(ctx, s, e);
 }
+
+} // namespace renderscript
+} // namespace android