Add RPC and UI for reachable size of an object / all instances of a class.

runtime/observatory/lib/src/elements/class_view.html

 <link rel="import" href="../../../../packages/polymer/polymer.html">
 <link rel="import" href="action_link.html">
 <link rel="import" href="cpu_profile.html">
 <link rel="import" href="curly_block.html">
 <link rel="import" href="eval_box.html">
 <link rel="import" href="eval_link.html">
 <link rel="import" href="field_ref.html">
 <link rel="import" href="function_ref.html">
 <link rel="import" href="instance_ref.html">
 <link rel="import" href="library_ref.html">
@@ skipping 163 matching lines @@
                   <eval-link callback="{{ reachable }}"
                            label="[more]"
                            expr="{{ instances['samples'].length * 2 }}">
                   </eval-link>
                 </template>
                 of total {{ instances['totalCount'] }}
               </template>
             </div>
           </div>
           <div class="memberItem">
+            <div class="memberName">total reachable memory size</div>
+            <div class="memberValue">
+              <template if="{{ reachableBytes == null }}">
+                <eval-link callback="{{ reachableSize }}"
+                           label="[calculate]">
+                </eval-link>
+              </template>
+              <template if="{{ reachableBytes != null }}">
+                {{ reachableBytes | formatSize }}
+              </template>
+            </div>
+          </div>
+          <div class="memberItem">
             <div class="memberName">total retained memory size</div>
             <div class="memberValue">
               <template if="{{ retainedBytes == null }}">
                 <eval-link callback="{{ retainedSize }}"
                            label="[calculate]">
                 </eval-link>
               </template>
               <template if="{{ retainedBytes != null }}">
                 {{ retainedBytes | formatSize }}
               </template>
@@ skipping 54 matching lines @@
       <hr>
       <source-inset location="{{ cls.location }}">
       </source-inset>
     </div>
 
     <view-footer></view-footer>
   </template>
 </polymer-element>
 
 <script type="application/dart" src="class_view.dart"></script>