[SPARK-9437] [CORE] avoid overflow in SizeEstimator

https://issues.apache.org/jira/browse/SPARK-9437

Author: Imran Rashid <irashid@cloudera.com>

Closes #7750 from squito/SPARK-9437_size_estimator_overflow and squashes the following commits:

29493f1 [Imran Rashid] prevent another potential overflow
bc1cb82 [Imran Rashid] avoid overflow

core/src/main/scala/org/apache/spark/util/SizeEstimator.scala

@@ -217,10 +217,10 @@ object SizeEstimator extends Logging {
     var arrSize: Long = alignSize(objectSize + INT_SIZE)
 
     if (elementClass.isPrimitive) {
-      arrSize += alignSize(length * primitiveSize(elementClass))
+      arrSize += alignSize(length.toLong * primitiveSize(elementClass))
       state.size += arrSize
     } else {
-      arrSize += alignSize(length * pointerSize)
+      arrSize += alignSize(length.toLong * pointerSize)
       state.size += arrSize
 
       if (length <= ARRAY_SIZE_FOR_SAMPLING) {
@@ -336,7 +336,7 @@ object SizeEstimator extends Logging {
     // hg.openjdk.java.net/jdk8/jdk8/hotspot/file/tip/src/share/vm/classfile/classFileParser.cpp
     var alignedSize = shellSize
     for (size <- fieldSizes if sizeCount(size) > 0) {
-      val count = sizeCount(size)
+      val count = sizeCount(size).toLong
       // If there are internal gaps, smaller field can fit in.
       alignedSize = math.max(alignedSize, alignSizeUp(shellSize, size) + size * count)
       shellSize += size * count