remove "prepareReact" call from the iOS bridge

Reviewed By: alexeylang

Differential Revision: D6581907

fbshipit-source-id: ca4bd4beef6d75305133a2b2c7de62e65e5aa3da

Author: fromcelticpark

React/CxxBridge/RCTCxxBridge.mm

@@ -739,6 +739,8 @@ - (void)executeSourceCode:(NSData *)sourceCode sync:(BOOL)sync
 {
   // This will get called from whatever thread was actually executing JS.
   dispatch_block_t completion = ^{
+    // Log start up metrics early before processing any other js calls
+    [self logStartupFinish];
     // Flush pending calls immediately so we preserve ordering
     [self _flushPendingCalls];
 
@@ -1013,16 +1015,19 @@ - (void)_runAfterLoad:(RCTPendingCall)block
   }
 }
 
-- (void)_flushPendingCalls
+- (void)logStartupFinish
 {
   // Log metrics about native requires during the bridge startup.
-  uint64_t nativeRequiresCount = [self->_performanceLogger valueForTag:RCTPLRAMNativeRequiresCount];
+  uint64_t nativeRequiresCount = [_performanceLogger valueForTag:RCTPLRAMNativeRequiresCount];
   [_performanceLogger setValue:nativeRequiresCount forTag:RCTPLRAMStartupNativeRequiresCount];
-  uint64_t nativeRequires = [self->_performanceLogger valueForTag:RCTPLRAMNativeRequires];
+  uint64_t nativeRequires = [_performanceLogger valueForTag:RCTPLRAMNativeRequires];
   [_performanceLogger setValue:nativeRequires forTag:RCTPLRAMStartupNativeRequires];
 
   [_performanceLogger markStopForTag:RCTPLBridgeStartup];
+}
 
+- (void)_flushPendingCalls
+{
   RCT_PROFILE_BEGIN_EVENT(0, @"Processing pendingCalls", @{ @"count": [@(_pendingCalls.count) stringValue] });
   // Phase B: _flushPendingCalls happens.  Each block in _pendingCalls is
   // executed, adding work to the queue, and _pendingCount is decremented.