More wordy comments about Neon

BUG=315
TESTED=untested
R=wuwang@google.com

Review URL: https://webrtc-codereview.appspot.com/9599004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@982 16f28f9a-4ce2-e073-06de-1de4eb20be90

README.chromium

 Name: libyuv
 URL: http://code.google.com/p/libyuv/
-Version: 981
+Version: 982
 License: BSD
 License File: LICENSE
 

include/libyuv/version.h

@@ -11,6 +11,6 @@
 #ifndef INCLUDE_LIBYUV_VERSION_H_  // NOLINT
 #define INCLUDE_LIBYUV_VERSION_H_
 
-#define LIBYUV_VERSION 981
+#define LIBYUV_VERSION 982
 
 #endif  // INCLUDE_LIBYUV_VERSION_H_  NOLINT

source/cpu_id.cc

@@ -122,7 +122,9 @@ LIBYUV_API SAFEBUFFERS
 int ArmCpuCaps(const char* cpuinfo_name) {
   FILE* f = fopen(cpuinfo_name, "r");
   if (!f) {
-    return kCpuHasNEON;  // Assume Neon if /proc/cpuinfo is unavailable.
+    // Assume Neon if /proc/cpuinfo is unavailable.
+    // This will occur for Chrome sandbox for Pepper or Render process.
+    return kCpuHasNEON;
   }
   char cpuinfo_line[512];
   while (fgets(cpuinfo_line, sizeof(cpuinfo_line) - 1, f)) {
@@ -248,10 +250,10 @@ int InitCpuFlags(void) {
     cpu_info_ &= ~kCpuHasMIPS_DSPR2;
   }
 #elif defined(__arm__)
+// gcc -mfpu=neon defines __ARM_NEON__
+// __ARM_NEON__ generates code that requires Neon.  NaCL also requires Neon.
+// For Linux, /proc/cpuinfo can be tested but without that assume Neon.
 #if defined(__ARM_NEON__) || defined(__native_client__) || !defined(__linux__)
-  // gcc -mfpu=neon defines __ARM_NEON__
-  // Enable Neon if you want support for Neon and Arm, and use MaskCpuFlags
-  // to disable Neon on devices that do not have it.
   cpu_info_ = kCpuHasNEON;
 #else
   // Linux arm parse text file for neon detect.