begin refactoring SkTDynamicHash and SkTMultiMap

The biggest mismatch between these and SkTHash{Map,Set,Table}
is the old ones provide Iter and ConstIter, the new ones foreach().

This CL,

   - adds foreach() methods to the old types,
   - replaces all uses of ConstIter with foreach(),
   - replaces most uses of Iter with foreach(),

I'm leaving one spot using Iter to walk the table and remove its
elements for its own CL... it'll be a little more complicated to get
that right.

From there it should be straightforward to turn SkTDynamicHash
into a thin wrapper over an SkTHashTable.

Bugs: skia:9703
Change-Id: Ia6ba87c35b89585c42b5b9f118f4cbf3abd04f0d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/277098
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
diff --git a/src/gpu/GrResourceCache.cpp b/src/gpu/GrResourceCache.cpp
index db0c878..d5d6b77 100644
--- a/src/gpu/GrResourceCache.cpp
+++ b/src/gpu/GrResourceCache.cpp
@@ -863,16 +863,13 @@
     };
 
     {
-        ScratchMap::ConstIter iter(&fScratchMap);
-
         int count = 0;
-        for ( ; !iter.done(); ++iter) {
-            const GrGpuResource* resource = *iter;
-            SkASSERT(resource->resourcePriv().getScratchKey().isValid());
-            SkASSERT(!resource->getUniqueKey().isValid());
+        fScratchMap.foreach([&](const GrGpuResource& resource) {
+            SkASSERT(resource.resourcePriv().getScratchKey().isValid());
+            SkASSERT(!resource.getUniqueKey().isValid());
             count++;
-        }
-        SkASSERT(count == fScratchMap.count()); // ensure the iterator is working correctly
+        });
+        SkASSERT(count == fScratchMap.count());
     }
 
     Stats stats(this);