Avoid growing boot class path for --single-image compiled images

Calculation of the number of components in Runtime::Init did not
account for images compiled with --single-image where the number of
images does not equal the number of components.

Bug: 160683548
Test: Treehugger
Change-Id: I1db7a4bbbc8bb2f48d54f5048bd1b8407d19cf02
diff --git a/runtime/image.h b/runtime/image.h
index 61db627..c8e5948 100644
--- a/runtime/image.h
+++ b/runtime/image.h
@@ -437,10 +437,12 @@
   // their oat files are mmapped independently.
   uint32_t image_reservation_size_ = 0u;
 
-  // The number of components.
+  // The number of components (jar files contributing to the image).
   // For boot image or boot image extension, the primary image stores the total number
-  // of images, secondary images have this set to 0.
-  // App images have 1 component.
+  // of components, secondary images have this set to 0. App images have 1 component.
+  // The component count usually matches the total number of images (one image per component), but
+  // if multiple components are compiled with --single-image there will only be 1 image associated
+  // with those components.
   uint32_t component_count_ = 0u;
 
   // Required base address for mapping the image.