Remove SkThread.h, include SkMutex.h or SkAtomics.h as appropriate.

SkThread.h doesn't do anything anymore execept include those two,
and thankfully, it doesn't seem to be mentioned outside Skia.

No public API changes.
TBR=reed@google.com

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/c50acf2321d7a934c80d754e9cbe936dfb8eb4cc

Review URL: https://codereview.chromium.org/1215393002
diff --git a/src/core/SkResourceCache.cpp b/src/core/SkResourceCache.cpp
index f0fe721..6c76d35 100644
--- a/src/core/SkResourceCache.cpp
+++ b/src/core/SkResourceCache.cpp
@@ -8,6 +8,7 @@
 #include "SkChecksum.h"
 #include "SkMessageBus.h"
 #include "SkMipMap.h"
+#include "SkMutex.h"
 #include "SkPixelRef.h"
 #include "SkResourceCache.h"
 
@@ -74,7 +75,7 @@
 
 class SkOneShotDiscardablePixelRef : public SkPixelRef {
 public:
-    
+
     // Ownership of the discardablememory is transfered to the pixelref
     SkOneShotDiscardablePixelRef(const SkImageInfo&, SkDiscardableMemory*, size_t rowBytes);
     ~SkOneShotDiscardablePixelRef();
@@ -236,7 +237,7 @@
 
 void SkResourceCache::add(Rec* rec) {
     this->checkMessages();
-    
+
     SkASSERT(rec);
     // See if we already have this key (racy inserts, etc.)
     Rec* existing = fHash->find(rec->getKey());
@@ -244,7 +245,7 @@
         SkDELETE(rec);
         return;
     }
-    
+
     this->addToHead(rec);
     fHash->add(rec);
 
@@ -357,7 +358,7 @@
 
 SkCachedData* SkResourceCache::newCachedData(size_t bytes) {
     this->checkMessages();
-    
+
     if (fDiscardableFactory) {
         SkDiscardableMemory* dm = fDiscardableFactory(bytes);
         return dm ? SkNEW_ARGS(SkCachedData, (bytes, dm)) : NULL;
@@ -515,8 +516,6 @@
 
 ///////////////////////////////////////////////////////////////////////////////
 
-#include "SkThread.h"
-
 SK_DECLARE_STATIC_MUTEX(gMutex);
 static SkResourceCache* gResourceCache = NULL;
 static void cleanup_gResourceCache() {