Refactor OS_LINUX preprocessor directive for LaCrOS effort.

Currently, ChromeOS defines the OS_LINUX directive as well as
OS_CHROMEOS.  We're working to separate these two, so we're
making the fact that OS_LINUX == OS_LINUX || OS_CHROMEOS
explicit.

This is changes for /base/allocator/partition_allocator

This CL was uploaded by git cl split.

R=lizeb@chromium.org

Bug: 1110266
Change-Id: Ibf15087393996835bdcedabeacec04114d96c6be
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2371209Reviewed-by: Benoit L <lizeb@chromium.org>
Commit-Queue: Sean McAllister <smcallis@google.com>
Cr-Commit-Position: refs/heads/master@{#801411}

base/allocator/partition_allocator/page_allocator_internals_posix.h

@@ -24,7 +24,7 @@
 #if defined(OS_ANDROID)
 #include <sys/prctl.h>
 #endif
-#if defined(OS_LINUX)
+#if defined(OS_LINUX) || defined(OS_CHROMEOS)
 #include <sys/resource.h>
 
 #include <algorithm>

base/allocator/partition_allocator/partition_alloc_unittest.cc

@@ -330,7 +330,7 @@ void FreeFullPage(PartitionRoot<base::internal::ThreadSafe>* root,
   }
 }
 
-#if defined(OS_LINUX)
+#if defined(OS_LINUX) || defined(OS_CHROMEOS)
 bool CheckPageInCore(void* ptr, bool in_core) {
   unsigned char ret = 0;
   EXPECT_EQ(0, mincore(ptr, kSystemPageSize, &ret));
@@ -341,7 +341,7 @@ bool CheckPageInCore(void* ptr, bool in_core) {
   EXPECT_TRUE(CheckPageInCore(ptr, in_core))
 #else
 #define CHECK_PAGE_IN_CORE(ptr, in_core) (void)(0)
-#endif  // defined(OS_LINUX)
+#endif  // defined(OS_LINUX) || defined(OS_CHROMEOS)
 
 class MockPartitionStatsDumper : public PartitionStatsDumper {
  public: