Make a new test to enforce the sizes of all structs and enums in the C API....

ppapi/c/ppb_var.h

Index: ppapi/c/ppb_var.h
===================================================================
--- ppapi/c/ppb_var.h	(revision 68374)
+++ ppapi/c/ppb_var.h	(working copy)
@@ -33,6 +33,7 @@
   PP_OBJECTPROPERTY_MODIFIER_DONTDELETE = 1 << 2,
   PP_OBJECTPROPERTY_MODIFIER_HASVALUE   = 1 << 3
 };
+PP_COMPILE_ASSERT_ENUM_SIZE_IN_BYTES(PP_ObjectProperty_Modifier, 4);
 
 struct PP_ObjectProperty {
   struct PP_Var name;
@@ -40,7 +41,16 @@
   struct PP_Var getter;
   struct PP_Var setter;
   uint32_t modifiers;
+
+  /** Ensure that this struct is 72 bytes wide by padding the end.  In some
+   *  compilers, PP_Var is 8-byte aligned, so those compilers align this struct
+   *  on 8-byte boundaries as well and pad it to 72 bytes even without this
+   *  padding attribute.  This padding makes its size consistent across
+   *  compilers.
+   */
+  int32_t padding;
 };
+PP_COMPILE_ASSERT_STRUCT_SIZE_IN_BYTES(PP_ObjectProperty, 72);
 
 /**
  * PPB_Var API