Refine systemInfo.cpu API defintions and provide systemInfo.cpu.get impl for Windows and Linux

base/win/windows_version.h

Index: base/win/windows_version.h
diff --git a/base/win/windows_version.h b/base/win/windows_version.h
index 0e4a75edd9ae025356b05a2f26142228f61010e5..e5dc3e659b03f09df2fd83b7950c39b238b41b42 100644
--- a/base/win/windows_version.h
+++ b/base/win/windows_version.h
@@ -76,6 +76,7 @@ class BASE_EXPORT OSInfo {
   int processors() const { return processors_; }
   size_t allocation_granularity() const { return allocation_granularity_; }
   WOW64Status wow64_status() const { return wow64_status_; }
+  std::string processor_model_name();
 
   // Like wow64_status(), but for the supplied handle instead of the current
   // process.  This doesn't touch member state, so you can bypass the singleton.
@@ -92,6 +93,7 @@ class BASE_EXPORT OSInfo {
   int processors_;
   size_t allocation_granularity_;
   WOW64Status wow64_status_;
+  std::string processor_model_name_;
 
   DISALLOW_COPY_AND_ASSIGN(OSInfo);
 };